Cluster-wide system clock in a multi-tiered full-graph interconnect architecture

ABSTRACT

Mechanisms for providing a cluster-wide system clock in a multi-tiered full graph (MTFG) interconnect architecture are provided. Heartbeat signals transmitted by each of the processor chips in the computing cluster are synchronized. Internal system clock signals are generated in each of the processor chips based on the synchronized heartbeat signals. As a result, the internal system clock signals of each of the processor chips are synchronized since the heartbeat signals, that are the basis for the internal system clock signals, are synchronized. Mechanisms are provided for performing such synchronization using direct couplings of processor chips within the same processor book, different processor books in the same supernode, and different processor books in different supernodes of the MTFG interconnect architecture.

GOVERNMENT RIGHTS

This invention was made with Government support under DARPA,HR0011-07-9-0002. THE GOVERNMENT HAS CERTAIN RIGHTS IN THIS INVENTION.

BACKGROUND

1. Technical Field

The present application relates generally to an improved data processingsystem and method. More specifically, the present application isdirected to a method for providing a cluster-wide system clock in amulti-tiered full-graph interconnect architecture for data processing.

2. Description of Related Art

Ongoing advances in distributed multi-processor computer systems havecontinued to drive improvements in the various technologies used tointerconnect processors, as well as their peripheral components. As thespeed of processors has increased, the underlying interconnect,intervening logic, and the overhead associated with transferring data toand from the processors have all become increasingly significant factorsimpacting performance. Performance improvements have been achievedthrough the use of faster networking technologies (e.g., GigabitEthernet), network switch fabrics (e.g., Infiniband, and RapidIO®), TCPoffload engines, and zero-copy data transfer techniques (e.g., remotedirect memory access). Efforts have also been increasingly focused onimproving the speed of host-to-host communications within multi-hostsystems. Such improvements have been achieved in part through the use ofhigh-speed network and network switch fabric technologies.

One type of multi-processor computer system known in the art is referredto as a “cluster” of data processing systems, or “computing cluster.” Acomputing cluster is a group of tightly coupled computers that worktogether closely so that in many respects they can be viewed as thoughthey are a single computer. The components of a cluster are commonly,but not always, connected to each other through fast local areanetworks. Clusters are usually deployed to improve performance and/oravailability over that provided by a single computer, while typicallybeing much more cost-effective than single computers of comparable speedor availability.

While computing clusters provide a way for separate computing devices towork in concert with each other, each of the computing devices itselfstill operates somewhat independently of the other computing devices inthe computing cluster and relies upon communication between thecomputing devices to provide the mechanism for collaborative computing.For example, each computing device still operates using its own internalsystem clock signal such that the system clock signals of the computingdevices in the computing cluster are not synchronized. As a result,operations which may require or benefit from synchronization of tasksbeing performed on the various computing devices must employ complexsynchronization mechanisms, typically provided in software outside thecircuitry of the computing devices. Such synchronization mechanisms tendto cause latencies and wasted processing cycles in the computing devicesas synchronization operations are performed or processors wait for otherprocessors to become synchronized.

SUMMARY

The illustrative embodiments provide a method for providing acluster-wide system clock in a multi-tiered full graph interconnectarchitecture. With the system and method of the illustrativeembodiments, the multi-tiered full graph (MTFG) interconnectarchitecture is configured as supernodes having one or more processorbooks which in turn have one or more processor chips coupled to oneanother. Routing mechanisms are provided for routing data betweenprocessor chips in the same processor book, in a different processorbook of a same supernode, and in a different processor book of adifferent supernode of the MTFG interconnect architecture. Buses areprovided between the processor chips, the processor books, and thesupernodes for transmission of data between the various elements.

These routing mechanisms may be utilized for routing a heartbeat signalto each of the processor chips within a defined computing cluster fromeach of the other processor chips directly coupled to the processorchip. In other words, each of the processor chips of a computing clustermay be initially synchronized through a heartbeat synchronizationprocess which involves a master processor chip, i.e. a processor chipinitiating the heartbeat synchronization process, distributing aheartbeat signal to each of the processor chips with which it isdirectly coupled, whether those processor chips be in the same book,same supernode, different book, or different supernode. The heartbeatsignal preferably includes a timestamp of when the heartbeat signal wastransmitted. This timestamp may be used by receiving processor chips todetermine a delay during transmission of the heartbeat signal such thatthe processor chips may predict when the next heartbeat signal from themaster processor chip may be transmitted.

The receiving processor chips then generate and transmit their ownheartbeat signal to their directly coupled processor chips at thepredicted time when the master processor chip sends its next heartbeatsignal. This process continues with each subsequent receiving processorchip until all of the processor chips in the computing cluster have beensynchronized based on the heartbeat signal to be transmitting theirheartbeat signals at the same time. For example, a sufficientpredetermined amount of time may be allowed to elapse, based on the sizeof the computing cluster and number of processor chips therein, topermit all of the processor chips in the computing cluster to becomesynchronized through the heartbeat signal mechanism.

Once synchronized in this manner, each of the processor chips may usethe heartbeat signal it generates to provide an internal system clock.The system clock may be used by the processor chips in timing theprocessing of instructions with processors of the processor chips. As aresult, operations being performed on each of the processor chips ineach of the processor books of each of the supernodes in a computingcluster may have their operations or tasks synchronized to the samecluster-wide system clock. This results in a reduction of wastedprocessor cycles waiting for operations or tasks to complete on otherprocessor chips and reduces latency in the overall computing cluster.

Even thought the system clocks of the processor chips may besynchronized in the above manner, over time the system clocks may driftout of synchronization due to any of a number of different factors.Thus, each processor chip may monitor the receipt of heartbeat signalsfrom its directly coupled processor chips to determine if any of theprocessor chip heartbeat signals drift significantly. That is, adifference between timestamps of received heartbeat signals and aheartbeat signal being generated by the processor chip may be determinedand compared to a threshold. If the threshold is exceeded, the aboveheartbeat synchronization process may be again performed to bring theprocessor chips back into synchronization. It should be appreciated thatthe heartbeat synchronization process in the MTFG interconnectarchitecture should require approximately three processor cycles tocomplete once initiated and thus, does not introduce a significantamount of overhead processing into the computing cluster.

In one illustrative embodiment, a method, in a computing clustercomprising a plurality of processor chips, for providing a cluster-widesystem clock signal is provided. The method may comprise synchronizingheartbeat signals transmitted by each of the processor chips in theplurality of processor chips such that each processor chip in theplurality of processor chips transmits a heartbeat signal atapproximately a same time. The method may further comprise generating,in each processor chip of the plurality of processor chips, an internalsystem clock signal based on a heartbeat signal transmitted by theprocessor chip. Through synchronization of the heartbeat signals, theinternal system clock signals of each processor chip of the plurality ofprocessor chips are synchronized.

The computing cluster may comprise a multi-tiered full graphinterconnect architecture data processing system having a plurality ofsupernodes. Each supernode may have one or more processor books. Eachprocessor book may have one or more processor chips of the plurality ofprocessor chips.

Synchronizing heartbeat signals transmitted by each of the processorchips may comprise transmitting, from a first processor chip, a firstheartbeat signal to at least one second processor chip directly coupledto the first processor chip and transmitting, in response to receivingthe first heartbeat signal, from the at least one second processor chip,a second heartbeat signal to at least one third processor chip directlycoupled to the at least one second processor chip. The second heartbeatsignal may be timed to be transmitted at approximately a same time asthe first heartbeat signal is re-transmitted to the at least one secondprocessor chip. Transmitting the first heartbeat signal to at least onesecond processor chip may comprise transmitting the first heartbeatsignal on the ports or phys associated with the first processor chip tosecond processor chips coupled to the ports or phys.

Transmitting the first heartbeat signal to at least one second processorchip may comprise performing a lookup operation in at least one routingtable data structure to identify second processor chips directly coupledto the first processor chip and transmitting the first heartbeat signalto second processor chips that are directly coupled to the firstprocessor chip based on results of the lookup operation. Performing thelookup operation may further comprise determining if a processor chipthat is directly coupled to the first processor chip is in an errorstate and eliminating the processor chip that is in an error state fromthe second processor chips.

Transmitting a second heartbeat signal may comprise predicting a time atwhich the first processor chip will re-transmit the first heartbeatsignal and timing the transmitting of the second heartbeat signal basedon the predicted time at which the first processor chip will re-transmitthe first heartbeat signal. The first heartbeat signal may include atimestamp of when the heartbeat signal was transmitted by the firstprocessor chip. Predicting a time at which the first processor chip willre-transmit the first heartbeat signal may comprise determining a delayduring transmission of the first heartbeat signal and using the delay topredict when the first heartbeat signal will be re-transmitted.

The method may be initiated in response to one of a user inputrequesting the method to be performed, a type of application or job thatis to be processed by the computing cluster, or a determination thatsynchronization of at least two processor chips in the computing clusterare sufficiently out of synchronization with each other. The heartbeatsignal may comprise header information identifying at least oneidentifier of a source processor chip of the heartbeat signal.

The method may further comprise using the internal system clock signalto time processing of instructions by processors of the processor chip.Moreover, the method may comprise monitoring, in each processor chip,receipt of heartbeat signals from directly coupled other processor chipsin the plurality of processor chips and determining if a heartbeatsignal from any of the directly coupled other processor chips is out ofsynchronization with a heartbeat signal of the processor chip. Themethod may also comprise initiating the synchronizing heartbeat signalsoperation in response to the determination indicating that a heartbeatsignal of a directly coupled other processor chip is out ofsynchronization with the heartbeat signal of the processor chip.Determining if a heartbeat signal from any of the directly coupled otherprocessor chips is out of synchronization with a heartbeat signal of theprocessor chip may comprise determining a difference in timestamps ofthe heartbeat signals and comparing the difference to a threshold. Ifthe difference is equal to or greater than the threshold, thesynchronizing heartbeat signals operation may be initiated.

The method may further comprise initiating, by a master processor chipin the plurality of processor chips, a heartbeat synchronizationoperation. Moreover, the method may comprise performing the heartbeatsynchronization operation and broadcasting an end of the heartbeatsynchronization operation in response to the performing of the heartbeatsynchronization operation being completed. Generating the internalsystem clock signal may be performed in response to receiving the end ofthe heartbeat synchronization operation. One or more processor chips inthe plurality of processor chips may be provided in a first processorbook and one or more processor chips in the plurality of processor chipsmay be provided in a second processor book. The first processor book maybe in a first supernode and the second processor book may be in a secondsupernode.

In other illustrative embodiments, a computer program product comprisinga computer useable medium having a computer readable program isprovided. The computer readable program, when executed on a computingdevice, causes the computing device to perform various ones, andcombinations of, the operations outlined above with regard to the methodillustrative embodiment.

In yet another illustrative embodiment, a system is provided. The systemmay comprise a processor and a memory coupled to the processor. Thememory may comprise instructions which, when executed by the processor,cause the processor to perform various ones, and combinations of, theoperations outlined above with regard to the method illustrativeembodiment.

These and other features and advantages of the present invention will bedescribed in, or will become apparent to those of ordinary skill in theart in view of, the following detailed description of the exemplaryembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, as well as a preferred mode of use and further objectivesand advantages thereof, will best be understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is an exemplary representation of an exemplary distributed dataprocessing system in which aspects of the illustrative embodiments maybe implemented;

FIG. 2 is a block diagram of an exemplary data processing system inwhich aspects of the illustrative embodiments may be implemented;

FIG. 3 depicts an exemplary logical view of a processor chip, which maybe a “node” in the multi-tiered full-graph interconnect architecture, inaccordance with one illustrative embodiment;

FIGS. 4A and 4B depict an example of such a multi-tiered full-graphinterconnect architecture in accordance with one illustrativeembodiment;

FIG. 5 depicts an example of direct and indirect transmissions ofinformation using a multi-tiered full-graph interconnect architecture inaccordance with one illustrative embodiment;

FIG. 6 depicts a flow diagram of the operation performed in the directand indirect transmissions of information using a multi-tieredfull-graph interconnect architecture in accordance with one illustrativeembodiment;

FIG. 7 depicts a fully non-blocking communication of information througha multi-tiered full-graph interconnect architecture network utilizingthe integrated switch/routers in the processor chips of the supernode inaccordance with one illustrative embodiment;

FIG. 8 depicts a flow diagram of the operation performed in the fullynon-blocking communication of information through a multi-tieredfull-graph interconnect architecture network utilizing the integratedswitch/routers (ISRs) in the processor chips of the supernode inaccordance with one illustrative embodiment;

FIG. 9 depicts an example of port connections between two elements of amulti-tiered full-graph interconnect architecture in order to provide areliability of communication between supernodes in accordance with oneillustrative embodiment;

FIG. 10 depicts a flow diagram of the operation performed in providing areliability of communication between supernodes in accordance with oneillustrative embodiment;

FIG. 11A depicts an exemplary method of integrated switch/routers (ISRs)utilizing routing information to route data through a multi-tieredfull-graph interconnect architecture network in accordance with oneillustrative embodiment;

FIG. 11B is a flowchart outlining an exemplary operation for selecting aroute based on whether or not the data has been previously routedthrough an indirect route to the current processor, in accordance withone illustrative embodiment;

FIG. 12 depicts a flow diagram of the operation performed to route datathrough a multi-tiered full-graph interconnect architecture network inaccordance with one illustrative embodiment;

FIG. 13 depicts an exemplary supernode routing table data structure thatsupports dynamic selection of routing within a multi-tiered full-graphinterconnect architecture using no-direct and no-indirect fields inaccordance with one illustrative embodiment;

FIG. 14A depicts a flow diagram of the operation performed in supportingthe dynamic selection of routing within a multi-tiered full-graphinterconnect architecture using no-direct and no-indirect fields inaccordance with one illustrative embodiment;

FIG. 14B outlines an exemplary operation for selecting a route fortransmitting data based on whether or not a no-direct or no-indirectindicator is set in accordance with one illustrative embodiment;

FIG. 15 is an exemplary diagram illustrating a computing clustercomprising supernodes, processor books, and processor chips inaccordance with the MTFG interconnect architecture of one illustrativeembodiment;

FIG. 16 is an exemplary diagram illustrating a first cycle of aheartbeat synchronization process executed in the computing cluster ofFIG. 15 in accordance with one illustrative embodiment;

FIG. 17 is an exemplary diagram illustrating a second cycle of aheartbeat synchronization process executed in the computing cluster ofFIG. 15 in accordance with one illustrative embodiment;

FIG. 18 is an exemplary diagram illustrating a third cycle of aheartbeat synchronization process executed in the computing cluster ofFIG. 15 in accordance with one illustrative embodiment;

FIG. 19 is an exemplary block diagram illustrating a processor chip withheartbeat synchronization logic in accordance with one illustrativeembodiment;

FIG. 20 is a flowchart outlining an exemplary operation in a processorchip for performing a heartbeat synchronization process in accordancewith one illustrative embodiment; and

FIG. 21 is a flowchart outlining an exemplary operation for monitoringheartbeat signals to determine if a heartbeat synchronization process isto be performed in accordance with one illustrative embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The illustrative embodiments provide an architecture and mechanisms forfacilitating communication between processors, or nodes, collections ofnodes, and supernodes. Furthermore, the illustrative embodiments providerouting mechanisms for routing communications directly or indirectlythrough the architecture and mechanisms for dynamic selection ofindirect and/or direct routes through the architecture. Moreover, theillustrative embodiments provide mechanisms for providing a cluster-widesystem clock for a plurality of processor chips in the same or differentcollections of processors on the same or different supernodes of thearchitecture.

As such, the mechanisms of the illustrative embodiments are especiallywell suited for implementation within a distributed data processingenvironment and within, or in association with, data processing devices,such as servers, client devices, and the like. In order to provide acontext for the description of the mechanisms of the illustrativeembodiments, FIGS. 1-2 are provided hereafter as examples of adistributed data processing system, or environment, and a dataprocessing device, in which, or with which, the mechanisms of theillustrative embodiments may be implemented. It should be appreciatedthat FIGS. 1-2 are only exemplary and are not intended to assert orimply any limitation with regard to the environments in which aspects orembodiments of the present invention may be implemented. Manymodifications to the depicted environments may be made without departingfrom the spirit and scope of the present invention.

With reference now to the figures, FIG. 1 depicts a pictorialrepresentation of an exemplary distributed data processing system inwhich aspects of the illustrative embodiments may be implemented.Distributed data processing system 100 may include a network ofcomputers in which aspects of the illustrative embodiments may beimplemented. The distributed data processing system 100 contains atleast one network 102, which is the medium used to provide communicationlinks between various devices and computers connected together withindistributed data processing system 100. The network 102 may includeconnections, such as wire, wireless communication links, or fiber opticcables.

In the depicted example, server 104 and server 106 are connected tonetwork 102 along with storage unit 108. In addition, clients 110, 112,and 114 are also connected to network 102. These clients 110, 112, and114 may be, for example, personal computers, network computers, or thelike. In the depicted example, server 104 provides data, such as bootfiles, operating system images, and applications to the clients 110,112, and 114. Clients 110, 112, and 114 are clients to server 104 in thedepicted example. Distributed data processing system 100 may includeadditional servers, clients, and other devices not shown.

In the depicted example, distributed data processing system 100 is theInternet with network 102 representing a worldwide collection ofnetworks and gateways that use the Transmission ControlProtocol/Internet Protocol (TCP/IP) suite of protocols to communicatewith one another. At the heart of the Internet is a backbone ofhigh-speed data communication lines between major nodes or hostcomputers, consisting of thousands of commercial, governmental,educational and other computer systems that route data and messages. Ofcourse, the distributed data processing system 100 may also beimplemented to include a number of different types of networks, such asfor example, an intranet, a local area network (LAN), a wide areanetwork (WAN), or the like. As stated above, FIG. 1 is intended as anexample, not as an architectural limitation for different embodiments ofthe present invention, and therefore, the particular elements shown inFIG. 1 should not be considered limiting with regard to the environmentsin which the illustrative embodiments of the present invention may beimplemented.

With reference now to FIG. 2, a block diagram of an exemplary dataprocessing system is shown in which aspects of the illustrativeembodiments may be implemented. Data processing system 200 is an exampleof a computer, such as client 110 in FIG. 1, in which computer usablecode or instructions implementing the processes for illustrativeembodiments of the present invention may be located.

In the depicted example, data processing system 200 employs a hubarchitecture including north bridge and memory controller hub (NB/MCH)202 and south bridge and input/output (I/O) controller hub (SB/ICH) 204.Processing unit 206, main memory 208, and graphics processor 210 areconnected to NB/MCH 202. Graphics processor 210 may be connected toNB/MCH 202 through an accelerated graphics port (AGP).

In the depicted example, local area network (LAN) adapter 212 connectsto SB/ICH 204. Audio adapter 216, keyboard and mouse adapter 220, modem222, read only memory (ROM) 224, hard disk drive (HDD) 226, CD-ROM drive230, universal serial bus (USB) ports and other communication ports 232,and PCI/PCIe devices 234 connect to SB/ICH 204 through bus 238 and bus240. PCI/PCIe devices may include, for example, Ethernet adapters,add-in cards, and PC cards for notebook computers. PCI uses a card buscontroller, while PCIe does not. ROM 224 may be, for example, a flashbinary input/output system (BIOS).

HDD 226 and CD-ROM drive 230 connect to SB/ICH 204 through bus 240. HDD226 and CD-ROM drive 230 may use, for example, an integrated driveelectronics (IDE) or serial advanced technology attachment (SATA)interface. Super I/O (SIO) device 236 may be connected to SB/ICH 204.

An operating system runs on processing unit 206. The operating systemcoordinates and provides control of various components within the dataprocessing system 200 in FIG. 2. As a client, the operating system maybe a commercially available operating system such as Microsoft® Windows®XP (Microsoft and Windows are trademarks of Microsoft Corporation in theUnited States, other countries, or both). An object-oriented programmingsystem, such as the Java™ programming system, may run in conjunctionwith the operating system and provides calls to the operating systemfrom Java™ programs or applications executing on data processing system200 (Java is a trademark of Sun Microsystems, Inc. in the United States,other countries, or both).

As a server, data processing system 200 may be, for example, an IBM®eServer™ System P™ computer system, running the Advanced InteractiveExecutive (AIXR) operating system or the LINUX® operating system(eServer, System P™ and AIX are trademarks of International BusinessMachines Corporation in the United States, other countries, or bothwhile LINUX is a trademark of Linus Torvalds in the United States, othercountries, or both). Data processing system 200 may be a symmetricmultiprocessor (SMP) system including a plurality of processors, such asthe POWER™ processor available from International Business MachinesCorporation of Armonk, N.Y., in processing unit 206. Alternatively, asingle processor system may be employed.

Instructions for the operating system, the object-oriented programmingsystem, and applications or programs are located on storage devices,such as HDD 226, and may be loaded into main memory 208 for execution byprocessing unit 206. The processes for illustrative embodiments of thepresent invention may be performed by processing unit 206 using computerusable program code, which may be located in a memory such as, forexample, main memory 208, ROM 224, or in one or more peripheral devices226 and 230, for example.

A bus system, such as bus 238 or bus 240 as shown in FIG. 2, may becomprised of one or more buses. Of course, the bus system may beimplemented using any type of communication fabric or architecture thatprovides for a transfer of data between different components or devicesattached to the fabric or architecture. A communication unit, such asmodem 222 or network adapter 212 of FIG. 2, may include one or moredevices used to transmit and receive data. A memory may be, for example,main memory 208, ROM 224, or a cache such as found in NB/MCH 202 in FIG.2.

Those of ordinary skill in the art will appreciate that the hardware inFIGS. 1-2 may vary depending on the implementation. Other internalhardware or peripheral devices, such as flash memory, equivalentnon-volatile memory, or optical disk drives and the like, may be used inaddition to or in place of the hardware depicted in FIGS. 1-2. Also, theprocesses of the illustrative embodiments may be applied to amultiprocessor data processing system, other than the SMP systemmentioned previously, without departing from the spirit and scope of thepresent invention.

Moreover, the data processing system 200 may take the form of any of anumber of different data processing systems including client computingdevices, server computing devices, a tablet computer, laptop computer,telephone or other communication device, a personal digital assistant(PDA), or the like. In some illustrative examples, data processingsystem 200 may be a portable computing device which is configured withflash memory to provide non-volatile memory for storing operating systemfiles and/or user-generated data, for example. Essentially, dataprocessing system 200 may be any known or later developed dataprocessing system without architectural limitation.

The illustrative embodiments provide a highly-configurable, scalablesystem that integrates computing, storage, networking, and software. Theillustrative embodiments provide for a multi-tiered full-graphinterconnect architecture that improves communication performance forparallel or distributed programs and improves the productivity of theprogrammer and system. The architecture is comprised of a plurality ofprocessors or nodes, that are associated with one another as acollection referred to as processor “books.” A processor “book” may bedefined as a collection of processor chips having local connections fordirect communication between the processors. A processor “book” mayfurther contain physical memory cards, one or more I/O hub cards, andthe like. The processor “books” are in turn in communication with oneanother via a first set of direct connections such that a collection ofprocessor books with such direct connections is referred to as a“supernode.” Supernodes may then be in communication with one anothervia external communication links between the supernodes. With such anarchitecture, and the additional mechanisms of the illustrativeembodiments described hereafter, a multi-tiered full-graph interconnectis provided in which maximum bandwidth is provided to each of theprocessors or nodes, such that enhanced performance of parallel ordistributed programs is achieved.

FIG. 3 depicts an exemplary logical view of a processor chip, which maybe a “node” in the multi-tiered full-graph interconnect architecture, inaccordance with one illustrative embodiment. Processor chip 300 may be aprocessor chip such as processing unit 206 of FIG. 2. Processor chip 300may be logically separated into the following functional components:homogeneous processor cores 302, 304, 306, and 308, and local memory310, 312, 314, and 316. Although processor cores 302, 304, 306, and 308and local memory 310, 312, 314, and 316 are shown by example, any typeand number of processor cores and local memory may be supported inprocessor chip 300.

Processor chip 300 may be a system-on-a-chip such that each of theelements depicted in FIG. 3 may be provided on a single microprocessorchip. Moreover, in an alternative embodiment processor chip 300 may be aheterogeneous processing environment in which each of processor cores302, 304, 306, and 308 may execute different instructions from each ofthe other processor cores in the system. Moreover, the instruction setfor processor cores 302, 304, 306, and 308 may be different from otherprocessor cores, that is, one processor core may execute ReducedInstruction Set Computer (RISC) based instructions while other processorcores execute vectorized instructions. Each of processor cores 302, 304,306, and 308 in processor chip 300 may also include an associated one ofcache 318, 320, 322, or 324 for core storage.

Processor chip 300 may also include an integrated interconnect systemindicated as Z-buses 328, L-buses 330, and D-buses 332. Z-buses 328,L-buses 330, and D-buses 332 provide interconnection to other processorchips in a three-tier complete graph structure, which will be describedin detail below. The integrated switching and routing provided byinterconnecting processor chips using Z-buses 328, L-buses 330, andD-buses 332 allow for network communications to devices usingcommunication protocols, such as a message passing interface (MPI) or aninternet protocol (IP), or using communication paradigms, such as globalshared memory, to devices, such as storage, and the like.

Additionally, processor chip 300 implements fabric bus 326 and other I/Ostructures to facilitate on-chip and external data flow. Fabric bus 326serves as the primary on-chip bus for processor cores 302, 304, 306, and308. In addition, fabric bus 326 interfaces to other on-chip interfacecontrollers that are dedicated to off-chip accesses. The on-chipinterface controllers may be physical interface macros (PHYs) 334 and336 that support multiple high-bandwidth interfaces, such as PCIx,Ethernet, memory, storage, and the like. Although PHYs 334 and 336 areshown by example, any type and number of PHYs may be supported inprocessor chip 300. The specific interface provided by PHY 334 or 336 isselectable, where the other interfaces provided by PHY 334 or 336 aredisabled once the specific interface is selected.

Processor chip 300 may also include host fabric interface (HFI) 338 andintegrated switch/router (ISR) 340. HFI 338 and ISR 340 comprise ahigh-performance communication subsystem for an interconnect network,such as network 102 of FIG. 1. Integrating HFI 338 and ISR 340 intoprocessor chip 300 may significantly reduce communication latency andimprove performance of parallel applications by drastically reducingadapter overhead. Alternatively, due to various chip integrationconsiderations (such as space and area constraints), HFI 338 and ISR 340may be located on a separate chip that is connected to the processorchip. HFI 338 and ISR 340 may also be shared by multiple processorchips, permitting a lower cost implementation. Processor chip 300 mayalso include symmetric multiprocessing (SMP) control 342 and collectiveacceleration unit (CAU) 344. Alternatively, these SMP control 342 andCAU 344 may also be located on a separate chip that is connected toprocessor chip 300. SMP control 342 may provide fast performance bymaking multiple cores available to complete individual processessimultaneously, also known as multiprocessing. Unlike asymmetricalprocessing, SMP control 342 may assign any idle processor core 302, 304,306, or 308 to any task and add additional ones of processor core 302,304, 306, or 308 to improve performance and handle increased loads. CAU344 controls the implementation of collective operations (collectives),which may encompass a wide range of possible algorithms, topologies,methods, and the like.

HFI 338 acts as the gateway to the interconnect network. In particular,processor core 302, 304, 306, or 308 may access HFI 338 over fabric bus326 and request HFI 338 to send messages over the interconnect network.HFI 338 composes the message into packets that may be sent over theinterconnect network, by adding routing header and other information tothe packets. ISR 340 acts as a router in the interconnect network. ISR340 performs three functions: ISR 340 accepts network packets from HFI338 that are bound to other destinations, ISR 340 provides HFI 338 withnetwork packets that are bound to be processed by one of processor cores302, 304, 306, and 308, and ISR 340 routes packets from any of Z-buses328, L-buses 330, or D-buses 332 to any of Z-buses 328, L-buses 330, orD-buses 332. CAU 344 improves the system performance and the performanceof collective operations by carrying out collective operations withinthe interconnect network, as collective communication packets are sentthrough the interconnect network. More details on each of these unitswill be provided further along in this application.

By directly connecting HFI 338 to fabric bus 326, by performing routingoperations in an integrated manner through ISR 340, and by acceleratingcollective operations through CAU 344, processor chip 300 eliminatesmuch of the interconnect protocol overheads and provides applicationswith improved efficiency, bandwidth, and latency.

It should be appreciated that processor chip 300 shown in FIG. 3 is onlyexemplary of a processor chip which may be used with the architectureand mechanisms of the illustrative embodiments. Those of ordinary skillin the art are well aware that there are a plethora of differentprocessor chip designs currently available, all of which cannot bedetailed herein. Suffice it to say that the mechanisms of theillustrative embodiments are not limited to any one type of processorchip design or arrangement and the illustrative embodiments may be usedwith any processor chip currently available or which may be developed inthe future. FIG. 3 is not intended to be limiting of the scope of theillustrative embodiments but is only provided as exemplary of one typeof processor chip that may be used with the mechanisms of theillustrative embodiments.

As mentioned above, in accordance with the illustrative embodiments,processor chips, such as processor chip 300 in FIG. 3, may be arrangedin processor “books,” which in turn may be collected into “supernodes.”Thus, the basic building block of the architecture of the illustrativeembodiments is the processor chip, or node. This basic building block isthen arranged using various local and external communication connectionsinto collections of processor books and supernodes. Local directcommunication connections between processor chips designate a processorbook. Another set of direct communication connections between processorchips enable communication with processor chips in other books. A fullyconnected group of processor books is called a supernode. In asupernode, there exists a direct communication connection between theprocessor chips in a particular book to processor chips in every otherbook. Thereafter, yet another different set of direct communicationconnections between processor chips enables communication to processorchips in other supernodes. The collection of processor chips, processorbooks, supernodes, and their various communication connections or linksgives rise to the multi-tiered full-graph interconnect architecture ofthe illustrative embodiments.

FIGS. 4A and 4B depict an example of such a multi-tiered full-graphinterconnect architecture in accordance with one illustrativeembodiment. In a data communication topology 400, processor chips 402,which again may each be a processor chip 300 of FIG. 3, for example, isthe main building block. In this example, a plurality of processor chips402 may be used and provided with local direct communication links tocreate processor book 404. In the depicted example, eight processorchips 402 are combined into processor book 404, although this is onlyexemplary and other numbers of processor chips, including only oneprocessor chip, may be used to designate a processor book withoutdeparting from the spirit and scope of the present invention. Forexample, any power of 2 number of processor chips may be used todesignate a processor book. In the context of the present invention, a“direct” communication connection or link means that the particularelement, e.g., a processor chip, may communicate data with anotherelement without having to pass through an intermediary element. Thus, an“indirect” communication connection or link means that the data ispassed through at least one intermediary element before reaching adestination element.

In processor book 404, each of the eight processor chips 402 may bedirectly connected to the other seven processor chips 402 via a bus,herein referred to as “Z-buses” 406 for identification purposes. FIG. 4Aindicates unidirectional Z-buses 406 connecting from only one ofprocessor chips 402 for simplicity. However, it should be appreciatedthat Z-buses 406 may be bidirectional and that each of processor chips402 may have Z-buses 406 connecting them to each of the other processorchips 402 within the same processor book. Each of Z-buses 406 mayoperate in a base mode where the bus operates as a network interfacebus, or as a cache coherent symmetric multiprocessing (SMP) bus enablingprocessor book 404 to operate as a 64-way (8 chips/book×8-way/chip) SMPnode. The terms “8-way,” “64-way”, and the like, refer to the number ofcommunication pathways a particular element has with other elements.Thus, an 8-way processor chip has 8 communication connections with otherprocessor chips. A 64-way processor book has 8 processor chips that eachhave 8 communication connections and thus, there are 8×8 communicationpathways. It should be appreciated that this is only exemplary and thatother modes of operation for Z-buses 406 may be used without departingfrom the spirit and scope of the present invention.

As depicted, a plurality of processor books 404, e.g., sixteen in thedepicted example, may be used to create supernode (SN) 408. In thedepicted SN 408, each of the sixteen processor books 404 may be directlyconnected to the other fifteen processor books 404 via buses, which arereferred to herein as “L-buses” 410 for identification purposes. FIG. 4Bindicates unidirectional L-buses 410 connecting from only one ofprocessor books 404 for simplicity. However, it should be appreciatedthat L-buses 410 may be bidirectional and that each of processor books404 may have L-buses 410 connecting them to each of the other processorbooks 404 within the same supernode. L-buses 410 may be configured suchthat they are not cache coherent, i.e. L-buses 410 may not be configuredto implement mechanisms for maintaining the coherency, or consistency,of caches associated with processor books 404.

It should be appreciated that, depending on the symmetric multiprocessor(SMP) configuration selected, SN 408 may have various SMP communicationconnections with other SNs. For example, in one illustrative embodiment,the SMP configuration may be set to either be a collection of 128 8-waySMP supernodes (SNs) or 16 64-way SMP supernodes. Other SMPconfigurations may be used without departing from the spirit and scopeof the present invention.

In addition to the above, in the depicted example, a plurality of SNs408 may be used to create multi-tiered full-graph (MTFG) interconnectarchitecture network 412. In the depicted example, 512 SNs are connectedvia external communication connections (the term “external” referring tocommunication connections that are not within a collection of elementsbut between collections of elements) to generate MTFG interconnectarchitecture network 412. While 512 SNs are depicted, it should beappreciated that other numbers of SNs may be provided with communicationconnections between each other to generate a MTFG without departing fromthe spirit and scope of the present invention.

In MTFG interconnect architecture network 412, each of the 512 SNs 408may be directly connected to the other 511 SNs 408 via buses, referredto herein as “D-buses” 414 for identification purposes. FIG. 4Bindicates unidirectional D-buses 414 connecting from only one of SNs 408for simplicity. However, it should be appreciated that D-buses 414 maybe bidirectional and that each of SNs 408 may have D-buses 414connecting them to each of the other SNs 408 within the same MTFGinterconnect architecture network 412. D-buses 414, like L-buses 410,may be configured such that they are not cache coherent.

Again, while the depicted example uses eight processor chips 402 perprocessor book 404, sixteen processor books 404 per SN 408, and 512 SNs408 per MTFG interconnect architecture network 412, the illustrativeembodiments recognize that a processor book may again contain othernumbers of processor chips, a supernode may contain other numbers ofprocessor books, and a MTFG interconnect architecture network maycontain other numbers of sup emodes. Furthermore, while the depictedexample considers only Z-buses 406 as being cache coherent, theillustrative embodiments recognize that L-buses 410 and D-buses 414 mayalso be cache coherent without departing from the spirit and scope ofthe present invention. Furthermore, Z-buses 406 may also be noncache-coherent. Yet again, while the depicted example shows athree-level multi-tiered full-graph interconnect, the illustrativeembodiments recognize that multi-tiered full-graph interconnects withdifferent numbers of levels are also possible without departing from thespirit and scope of the present invention. In particular, the number oftiers in the MTFG interconnect architecture could be as few as one or asmany as may be implemented. Thus, any number of buses may be used withthe mechanisms of the illustrative embodiments. That is, theillustrative embodiments are not limited to requiring Z-buses, D-buses,and L-buses. For example, in an illustrative embodiment, each processorbook may be comprised of a single processor chip, thus, only L-buses andD-buses are utilized. The example shown in FIGS. 4A and 4B is only forillustrative purposes and is not intended to state or imply anylimitation with regard to the numbers or arrangement of elements otherthan the general organization of processors into processor books,processor books into supernodes, and supernodes into a MTFG interconnectarchitecture network.

Taking the above described connection of processor chips 402, processorbooks 404, and SNs 408 as exemplary of one illustrative embodiment, theinterconnection of links between processor chips 402, processor books404, and SNs 408 may be reduced by at least fifty percent when comparedto externally connected networks, i.e. networks in which processorscommunicate with an external switch in order to communicate with eachother, while still providing the same bisection of bandwidth for allcommunication. Bisection of bandwidth is defined as the minimumbi-directional bandwidths obtained when the multi-tiered full-graphinterconnect is bisected in every way possible while maintaining anequal number of nodes in each half. That is, known systems, such assystems that use fat-tree switches, which are external to the processorchip, only provide one connection from a processor chip to the fat-treeswitch. Therefore, the communication is limited to the bandwidth of thatone connection. In the illustrative embodiments, one of processor chips402 may use the entire bisection of bandwidth provided throughintegrated switch/router (ISR) 416, which may be ISR 340 of FIG. 3, forexample, to either:

-   -   communicate to another processor chip 402 on a same processor        book 404 where processor chip 402 resides via Z-buses 406,    -   communicate to another processor chip 402 on a different        processor book 404 within a same SN 408 via L-buses 410, or    -   communicate to another processor chip 402 in another processor        book 404 in another one of SNs 408 via D-buses 414.

That is, if a communicating parallel “job” being run by one of processorchips 402 hits a communication point, i.e. a point in the processing ofa job where communication with another processor chip 402 is required,then processor chip 402 may use any of the processor chip's Z-buses 406,L-buses 410, or D-buses 414 to communicate with another processor aslong as the bus is not currently occupied with transferring other data.Thus, by moving the switching capabilities inside the processor chipitself instead of using switches external to the processor chip, thecommunication bandwidth provided by the multi-tiered full-graphinterconnect architecture of data communication topology 400 is maderelatively large compared to known systems, such as the fat-tree switchbased network which again, only provides a single communication linkbetween the processor and an external switch complex.

FIG. 5 depicts an example of direct and indirect transmissions ofinformation using a multi-tiered full-graph interconnect architecture inaccordance with one illustrative embodiment. It should be appreciatedthat the term “direct” as it is used herein refers to using a singlebus, whether it be a Z-bus, L-bus, or D-bus, to communicate data from asource element (e.g., processor chip, processor book, or supernode), toa destination or target element (e.g., processor chip, processor book,or supernode). Thus, for example, two processor chips in the sameprocessor book have a direct connection using a single Z-bus. Twoprocessor books have a direct connection using a single L-bus. Twosupernodes have a direct connection using a single D-bus. The term“indirect” as it is used herein refers to using a plurality of buses,i.e. any combination of Z-buses, L-buses, and/or D-buses, to communicatedata from a source element to a destination or target element. The termindirect refers to the usage of a path that is longer than the shortestpath between two elements.

FIG. 5 illustrates a direct connection with respect to the D-bus 530 andan indirect connection with regard to D-buses 550 and 556. As shown inthe example depicted in FIG. 5, in multi-tiered full-graph (MTFG)interconnect architecture 500, processor chip 502 transmits information,e.g., a data packet or the like, to processor chip 504 via Z-buses,L-buses, and D-buses. For simplicity in illustrating direct and indirecttransmissions of information, supernode (SN) 508 is shown to includeprocessor books 506 and 510 for simplicity of the description, while theabove illustrative embodiments show that a supernode may includenumerous books. Likewise, processor book 506 is shown to includeprocessor chip 502 and processor chip 512 for simplicity of thedescription, while the above illustrative embodiments indicate that aprocessor book may include numerous processor chips.

As an example of a direct transmission of information, processor chip502 initializes the transmission of information to processor chip 504 byfirst transmitting the information on Z-bus 514 to processor chip 512.Then, processor chip 512 transmits the information to processor chip 516in processor book 510 via L-bus 518. Processor chip 516 transmits theinformation to processor chip 520 via Z-bus 522 and processor chip 520transmits the information to processor chip 524 in processor book 526 ofSN 528 via D-bus 530. Once the information arrives in processor chip524, processor chip 524 transmits the information to processor chip 532via Z-bus 534. Processor chip 532 transmits the information to processorchip 536 in processor book 538 via L-bus 540. Finally, processor chip536 transmits the information to processor chip 504 via Z-bus 542. Eachof the processor chips, in the path the information follows fromprocessor chip 502 to processor chip 504, determines its own routingusing routing table topology that is specific to each processor chip.This direct routing table topology will be described in greater detailhereafter with reference to FIG. 15. Additionally, the exemplary directpath is the longest direct route, with regard to the D-bus, that ispossible in the depicted system within the routing scheme of theillustrative embodiments.

As an example of an indirect transmission of information, with regard tothe D-buses, processor chip 502 generally transmits the informationthrough processor chips 512 and 516 to processor chip 520 in the samemanner as described above with respect to the direct transmission ofinformation. However, if D-bus 530 is not available for transmission ofdata to processor chip 524, or if the full outgoing interconnectbandwidth from SN 508 were desired to be utilized in the transmission,then processor chip 520 may transmit the information to processor chip544 in processor book 546 of SN 548 via D-bus 550. Once the informationarrives in processor chip 544, processor chip 544 transmits theinformation to processor chip 552 via Z-bus 554. Processor chip 552transmits the information to processor chip 556 in processor book 558via L-bus 560. Processor chip 556 then transmits the information toprocessor chip 562 via Z-bus 564 and processor chip 562 transmits theinformation to processor chip 524 via D-bus 566. Once the informationarrives in processor chip 524, processor chip 524 transmits theinformation through processor chips 532 and 536 to processor chip 504 inthe same manner as described above with respect to the directtransmission of information. Again, each of the processor chips, in thepath the information follows from processor chip 502 to processor chip504, determines its own routing using routing table topology that isspecific to each processor chip. This indirect routing table topologywill be described in greater detail hereafter with reference to FIG. 15.

Thus, the exemplary direct and indirect transmission paths provide themost non-limiting routing of information from processor chip 502 toprocessor chip 504. What is meant by “non-limiting” is that thecombination of the direct and indirect transmission paths provide theresources to provide full bandwidth connections for the transmission ofdata during substantially all times since any degradation of thetransmission ability of one path will cause the data to be routedthrough one of a plurality of other direct or indirect transmissionpaths to the same destination or target processor chip. Thus, theability to transmit data is not limited when paths become available dueto the alternative paths provided through the use of direct and indirecttransmission paths in accordance with the illustrative embodiments.

That is, while there may be only one minimal path available to transmitinformation from processor chip 502 to processor chip 504, restrictingthe communication to such a path may constrain the bandwidth availablefor the two chips to communicate. Indirect paths may be longer thandirect paths, but permit any two communicating chips to utilize manymore of the paths that exist between them. As the degree of indirectnessincreases, the extra links provide diminishing returns in terms ofuseable bandwidth. Thus, while the direct route from processor chip 502to processor chip 504 shown in FIG. 5 uses only 7 links, the indirectroute from processor chip 502 to processor chip 504 shown in FIG. 5 uses11 links. Furthermore, it will be understood by one skilled in the artthat when processor chip 502 has more than one outgoing Z-bus, it coulduse those to form an indirect route. Similarly, when processor chip 502has more than one outgoing L-bus, it could use those to form indirectroutes.

Thus, through the multi-tiered full-graph interconnect architecture ofthe illustrative embodiments, multiple direct communication pathwaysbetween processors are provided such that the full bandwidth ofconnections between processors may be made available for communication.Moreover, a large number of redundant, albeit indirect, pathways may beprovided between processors for use in the case that a direct pathway isnot available, or the full bandwidth of the direct pathway is notavailable, for communication between the processors.

By organizing the processor chips, processor books, and supernodes in amulti-tiered full-graph arrangement, such redundancy of pathways is madepossible. The ability to utilize the various communication pathwaysbetween processors is made possible by the integrated switch/router(ISR) of the processor chips which selects a communication link overwhich information is to be transmitted out of the processor chip. Eachof these ISRs, as will be described in greater detail hereafter, storesone or more routing tables that are used to select between communicationlinks based on previous pathways taken by the information to becommunicated, current availability of pathways, available bandwidth, andthe like. The switching performed by the ISRs of the processor chips ofa supernode is performed in a fully non-blocking manner. By “fullynon-blocking” what is meant is that it never leaves any potentialswitching bandwidth unused if possible. If an output link has availablecapacity and there is a packet waiting on an input link to go to it, theISR will route the packet if possible. In this manner, potentially asmany packets as there are output links get routed from the input links.That is, whenever an output link can accept a packet, the switch willstrive to route a waiting packet on an input link to that output link,if that is where the packet needs to be routed. However, there may bemany qualifiers for how a switch operates that may limit the amount ofusable bandwidth.

FIG. 6 depicts a flow diagram of the operation performed in the directand indirect transmissions of information using a multi-tieredfull-graph interconnect architecture in accordance with one illustrativeembodiment. FIGS. 6, 8, 10, 11B, 12, 14A, 14B, 16, 18, 20, and 22 areflowcharts that illustrate the exemplary operations according to theillustrative embodiments. It will be understood that each block of theflowchart illustrations, and combinations of blocks in the flowchartillustrations, may be implemented by computer program instructions.These computer program instructions may be provided to a processor orother programmable data processing apparatus to produce a machine, suchthat the instructions which execute on the processor or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the flowchart block or blocks. These computerprogram instructions may also be stored in a computer-readable memory orstorage medium that can direct a processor or other programmable dataprocessing apparatus to function in a particular manner, such that theinstructions stored in the computer-readable memory or storage mediumproduce an article of manufacture including instruction means whichimplement the functions specified in the flowchart block or blocks.

Accordingly, blocks of the flowchart illustrations support combinationsof means for performing the specified functions, combinations of stepsfor performing the specified functions and program instruction means forperforming the specified functions. It will also be understood that eachblock of the flowchart illustrations, and combinations of blocks in theflowchart illustrations, can be implemented by special purposehardware-based computer systems which perform the specified functions orsteps, or by combinations of special purpose hardware and computerinstructions.

Furthermore, the flowcharts are provided to demonstrate the operationsperformed within the illustrative embodiments. The flowcharts are notmeant to state or imply limitations with regard to the specificoperations or, more particularly, the order of the operations. Theoperations of the flowcharts may be modified to suit a particularimplementation without departing from the spirit and scope of thepresent invention.

With regard to FIG. 6, the operation begins when a source processorchip, such as processor chip 502 of FIG. 5, in a first supernodereceives information, e.g., a data packet or the like, that is to betransmitted to a destination processor chip via buses, such as Z-buses,L-buses, and D-buses (step 602). The integrated switch/router (ISR) thatis associated with the source processor chip analyzes user input,current network conditions, packet information, routing tables, or thelike, to determine whether to use a direct pathway or an indirectpathway from the source processor chip to the destination processor chipthrough the multi-tiered full-graph architecture network (step 604). TheISR next checks if a direct path is to be used or if an indirect path isto be used (step 606).

Here, the terms “direct” and “indirect” may be with regard to any one ofthe buses, Z-bus, L-bus, or D-bus. Thus, if the source and destinationprocessor chips are within the same processor book, a direct pathbetween the processor chips may be made by way of a Z-bus. If the sourceand destination processor chips are within the same supernode, either adirect path using a single L-bus may be used or an indirect path usingone or more Z and L-buses (that is longer than the shortest pathconnecting the source and destination) may be used. Similarly, if thesource and destination processor chips are in separate supernodes,either a direct path using a single D-bus may be used (which may stillinvolve one or more Z and L-buses to get the data out of the sourcesupernode and within the destination supernode to get the data to thedestination processor chip) or an indirect path using a plurality ofD-paths (where such a path is indirect because it uses more buses thanrequired in the shortest path between the source and the destination)may be used.

If at step 606 a direct pathway is determined to have been chosen totransmit from the source processor chip to the destination processorchip, the ISR identifies the initial component of the direct path to usefor transmission of the information from the source processor chip tothe destination supernode (step 608). If at step 606 an indirect pathwayis determined to have been chosen to transmit from the source processorchip to the destination processor chip, the ISR identifies the initialcomponent of the indirect path to use for transmission of theinformation from the source processor chip to an intermediate supernode(step 610). From step 608 or 610, the ISR initiates transmission of theinformation from the source processor chip along the identified director indirect pathway (step 612). After the ISR of the source processorchip transmits the data to the last processor chip along the identifiedpath, the ISR of the processor chip where the information residesdetermines if it is the destination processor chip (step 614). If atstep 614 the ISR determines that the processor chip where theinformation resides is not the destination processor chip, the operationreturns to step 602 and may be repeated as necessary to move theinformation from the point to which it has been transmitted, to thedestination processor chip.

If at step 614, the processor chip where the information resides is thedestination processor chip, the operation terminates. An example of adirect transmission of information and an indirect transmission ofinformation is shown in FIG. 5 above. Thus, through the multi-tieredfull-graph interconnect architecture of the illustrative embodiments,information may be transmitted from a one processor chip to anotherprocessor chip using multiple direct and indirect communication pathwaysbetween processors.

FIG. 7 depicts a fully non-blocking communication of information througha multi-tiered full-graph interconnect architecture utilizing theintegrated switch/routers in the processor chips of the supernode inaccordance with one illustrative embodiment. In this example, processorchip 702, which may be an example of processor chip 502 of FIG. 5, forexample, transmits information to processor chip 704, which may beprocessor chip 504 of FIG. 5, for example, via L-buses and D-buses, andprocessor chips 710-722. For simplicity in illustrating direct andindirect transmissions of information in this example, only the L-busesand D-buses are shown in order to illustrate the routing from aprocessor chip of one processor book of a supernode to another processorchip of another processor book of another supernode. It should beappreciated that additional routing operations may be performed within aprocessor book as will be described in greater detail hereafter.

In the depicted example, in order to transmit information from a sourceprocessor chip 702 to a destination processor chip 704 through indirectroute 706, as in the case of the indirect route (that ignores theZ-buses) shown in FIG. 5, there is a minimum of five virtual channels,VC₁, VC₂, VC₃, VC₄, and VC₅, in a switch, such as integratedswitch/router 340 of FIG. 3, for each processor chip required totransmit the information and provide a fully non-blocking switch system.The virtual channels may be any type of data structure, such as abuffer, a queue, and the like, that represents a communicationconnection with another processor chip. The switch provides the virtualchannels for each port of the processor chip, allocating one VC forevery hop of the longest route in the network. For example, for aprocessor chip, such as processor chip 402 of FIG. 4A, that has eightZ-buses, four D-buses, and two L-buses, where the longest indirect pathis (voluntarily) constrained to be ZLZDZLZDZLZ, the ISR will provideeleven virtual channels for each port for a total of one-hundred andfifty four virtual channels per processor chip. Each of the virtualchannels within the ISR are at different levels and each level is usedby the specific processor chip based on the position of the specificprocessor chip within the route the information is taking from a sourceprocessor chip to a destination processor chip.

For indirect route 706 transmission, processor chip 702 stores theinformation in VC₁ 708 since processor chip 702 is the source of theinformation being transmitted. When the information is transmitted fromprocessor chip 702 to processor chip 710, the ISR of processor chip 710stores the information in VC₂ 712 since processor chip 710 is the second“hop” in the path the information is being transmitted. Headerinformation in the data packets or the like, that make up theinformation being transmitted may maintain hop identificationinformation, e.g., a counter or the like, by which the ISRs of theprocessor chips may determine in which VC to place the information. Sucha counter may be incremented with each hop along indirect route 706. Inanother alternative embodiment, identifiers of the processor chips thathave handled the information during its path from processor chip 702 toprocessor chip 704 may be added to the header information.

When the information is transmitted from processor chip 710 to processorchip 714, the ISR of processor chip 714 stores the information in VC₃716. When the information is transmitted from processor chip 714 toprocessor chip 718, the ISR of processor chip 718 stores the informationin VC₄ 720. And finally, when the information is transmitted fromprocessor chip 718 to processor chip 722, the ISR of processor chip 722stores the information in VC₅ 724. Then, the information is transmittedfrom processor chip 722 to processor chip 704 where processor chip 704processes the information and thus, it is not necessary to maintain theinformation in a VC data structure.

As an example of direct route transmission, with regard to the D-bus, inorder to transmit information from processor chip 702 to processor chip704 through direct route 726, as in the case of the direct route shownin FIG. 5, three virtual channels VC₁, VC₂, and VC₃ are used to transmitthe information and provide a fully non-blocking switch system. Fordirect route 726 transmission, the ISR of processor chip 702 stores theinformation in VC₁ 708. When the information is transmitted fromprocessor chip 702 to processor chip 710, the ISR of processor chip 710stores the information in VC₂ 712. When the information is transmittedfrom processor chip 710 to processor chip 722, the ISR of processor chip722 stores the information in VC₃ 728. Then the information istransmitted from processor chip 722 to processor chip 704 whereprocessor chip 704 processes the information and thus, does not maintainthe information in a VC data structure.

These principles are codified in the following exemplary pseudocodealgorithm that is used to select virtual channels. Here, VCZ, VCD, andVCL represent the virtual channels pre-allocated for the Z, L, and Dports respectively.

** VC's are used to prevent deadlocks in the network. ** ** 6 VC's areused for Z-ports, 3 VC's are used for L-ports, and 2 VC's are used forD-ports in this exemplary pseudocode. ** ** Exemplary VC selectionAlgorithm **   next_Z = next_L = next_D = 0   for each hop    if hop isZ      VCZ = next_Z++    if hop is L      next_Z = next_L * 2 + 1     VCL = next_L++    if hop is D      next_Z = next_D * 2 + 2     next_L = next_D + 1      VCD = next_D++

Thus, the number of virtual channels needed to transmit information froma source processor chip to a destination processor chip is dependent onthe number of processor chips in the route from the source processorchip to the destination processor chip. The number of virtual channelsthat are available for use may be hardcoded in the switch architecture,or may be dynamically allocated up to a maximum pre-determined number ofVCs based on an architecture discovery operation, or the like. Thenumber of virtual channels that are provided for in the ISRs determinesthe maximum hop count of any route in the system. Thus, a MTFGinterconnect architecture may require any number of virtual channels perprocessor chip, such as three, five, seven, nine, or the like. Providingthe appropriate amount of virtual channels allows for the most efficientuse of a fully bisectional bandwidth network while providing a fullynon-blocking switch system.

Additionally, each of the virtual channels must be of sufficient depth,so that, the switch operates in a non-blocking manner. That is, thedepth or size of the virtual channels may be dynamically changed by theISRs so that, if half of the processor chips in the network aretransmitting information and half of the processor chips in the networkare receiving information, then the ISRs may adjust the depth of eachvirtual channel such the that network operates in a fully non-blockingmanner. Allocating the depth or the size of the virtual channels may beachieved, for example, by statically allocating a minimum number ofbuffers to each virtual channel and then dynamically allocating theremainder from a common pool of buffers, based on need.

In order to provide communication pathways between processors or nodes,processor books, and supernodes, a plurality of redundant communicationlinks are provided between these elements. These communication links maybe provided as any of a number of different types of communication linksincluding optical fibre links, wires, or the like. The redundancy of thecommunication links permits various reliability functions to beperformed so as to ensure continued operation of the MTFG interconnectarchitecture network even in the event of failures.

FIG. 8 depicts a flow diagram of the operation performed in the fullynon-blocking communication of information through a multi-tieredfull-graph interconnect architecture utilizing the integratedswitch/routers in the processor chips of the sup emode in accordancewith one illustrative embodiment. As the operation begins, an integratedswitch/router (ISR), such as ISR 340 of FIG. 3, of a source processorchip receives information that is to be transmitted to a destinationprocessor chip (step 802). Using the routing tables (e.g., see FIG. 11Adescribed hereafter), each ISR along a route from the source processorchip to the destination processor chip identifies a pathway fortransmitting the information from itself to a next processor chip alongthe pathway (step 804). The ISR(s) then transmit the information alongthe pathway from the source processor chip to the destination processorchip (step 806). As the information is transmitted along the pathway,each ISR stores the information in the virtual channels that isassociated with its position along the pathway from the source processorchip to the destination processor chip until the information arrives atthe destination processor chip (step 808), with the operation endingthereafter.

Thus, the number of virtual channels needed to transmit information froma source processor chip to a destination processor chip is dependent onthe number of processor chips in the route from the source processorchip to the destination processor chip.

FIG. 9 depicts an example of port connections between two elements of amulti-tiered full-graph interconnect architecture in order to provide areliability of communication between supernodes in accordance with oneillustrative embodiment. It should be appreciated that FIG. 9 shows adirect connection between processor chips 902 and 904, however similarconnections may be provided between a plurality of processor chips in achain formation. Moreover, each processor chip may have separatetransceivers 908 and communication links 906 for each possible processorchip with which it is directly connected.

With the illustrative embodiments, for each port, either Z-bus, D-bus,or L-bus, originating from a processor chip, such as processor chip 402of FIG. 4A, there may be one or more optical fibers, wires, or othertype of communication link, that connects to one or more processor chipsin the same or different processor book or the same or a differentsupernode of the multi-tiered full-graph (MTFG) interconnectarchitecture network. In the case of optical fibers, there may beinstances during manufacturing, shipping, usage, adjustment, or thelike, where the one or more optical fibers may not work all of the time,thereby reducing the number of optical fiber lanes available to theprocessor chip and to the fully bisectional bandwidth available to theMTFG interconnect architecture network. In the event that one or more ofthe optical fiber lanes are not available due to one or more opticalfibers not working for some reason, the MTFG interconnect architecturesupports identifying the various non-available optical fiber lanes andusing the port but at a reduced capacity since one or more of theoptical fiber lanes is not available.

Additionally, the MTFG interconnect architecture supports identifyingoptical fiber lanes, as well as wired lanes, that are experiencing higherrors as determined by performing error correction code (ECC) or cyclicredundancy checking (CRC). In performing ECC, data that is being read ortransmitted may be checked for errors and, when necessary, the data maybe corrected on the fly. In cyclic redundancy checking (CRC), data thathas been transmitted on the optical fiber lanes or wired lanes ischecked for errors. With ECC or CRC, if the error rates are too highbased on a predetermined threshold value, then the MTFG interconnectarchitecture supports identifying the optical fiber lanes or the wiredlanes as unavailable and the port is still used but at a reducedcapacity since one or more of the lanes is unavailable.

An illustration of the identification of optical fiber lanes or wiredlanes as unavailable may be made with reference to FIG. 9. As shown inFIG. 9, processor chips 902 and 904 are connected bi-directionally bycommunication links 906, which may be a multi-fiber (at least one fiber)optical link or a multi-wire (at least one wire) link. ISR 912associated with transceivers 908, which may be PHY 334 or 336 of theprocessor chip 300 in FIG. 3, for example, on processor chip 902 retainscharacteristic information of the particular one of communication links906 on which the transceiver 908 receives information from processorchip 904. Likewise, ISR 914 associated with transceiver 910 on processorchip 904 retains the characteristic information of the particular one ofcommunication links 906 on which transceiver 910 receives informationfrom processor chip 902. These “characteristics” represent the currentstate of communication links 906, e.g., traffic across the communicationlink, the ECC and CRC information indicating a number of errorsdetected, and the like.

For example, the characteristic information may be maintained in one ormore routing table data structures maintained by the ISR, or in anotherdata structure, in association with an identifier of the communicationlink. In this way, this characteristic information may be utilized byISR 912 or 914 in selecting which transceivers and communication linksover which to transmit information/data. For example, if a particularcommunication link is experiencing a large number of errors, asdetermined from the ECC and CRC information and a permissible thresholdof errors, then that communication link may no longer be used by ISR 912or 914 when transmitting information to the other processor chip.Instead, the other transceivers and communication links may be selectedfor use while eliminating the communication link and transceiverexperiencing the excessive error of data traffic.

When formatting the information for transmission over communicationlinks 906, ISR 912 or 914 augments each packet of data transmitted fromprocessor chip 902 to processor chip 904 with header information andECC/CRC information before being broken up into chunks that have as manybits as the number of communication links 906 currently used tocommunicate data from processor chip 902 to processor chip 904. ISR 912in processor chip 902 arranges the chunks such that all bits transmittedover a particular link over some period of time include both 0's and1's. This may be done, for example, by transmitting the 1's complementof the data instead of the original data and specifying the same in theheader.

In processor chip 904, ISR 914 receives the packets and uses the CRC inthe received packets to determine which bit(s) are in error. ISR 914identifies and records the corresponding one of communication links 906on which those bits were received. If transceivers 910 receive only 0'sor 1's over one of communication links 906 over a period of time, ISR914 may tag the corresponding transceiver as being permanently failed inits data structures. If a particular one of communication links 906 hasan error rate that is higher than a predetermined, or user-specified,threshold, ISR 914 may tag that link as being temporarily error prone inits data structures. Error information of this manner may be collectedand aggregated over predetermined, or user-specified, intervals.

ISR 914 may transmit the collected information periodically back to thesending processor chip 902. At the sender, ISR 912 uses the collectedinformation to determine which of communication links 906 will be usedto transmit information over the next interval.

To capture conditions where a link may be stuck at 0 or 1 for prolongedperiods of times (but not permanently), transceivers 908 and 910periodically transmit information over all of communication links 906that exist on a particular point to point link between it and areceiving node. ISRs 912 and 914 may use the link state information sentback by transceivers 908 and 910 to recover from transient errorconditions.

Again, in addition to identifying individual links between processorchips that may be in a state where they are unusable, e.g., an errorstate or permanent failure state, ISRs 912 and 914 of processor chips902 and 904 select which set of links over which to communicate theinformation based on routing table data structures and the like. Thatis, there may be a set of communication links 906 for each processorchip with which a particular processor chip 902 has a direct connection.That is, there may be a set of communication links 906 for each of theL-bus, Z-bus, and D-bus links between processor chips. The particularL-bus, Z-bus, and/or D-bus link to utilize in routing the information tothe next processor chip in order to get the information to an intendedrecipient processor chip is selected by ISRs 912 and 914 using therouting table data structures while the particular links of the selectedL-bus, Z-bus, and/or D-bus that are used to transmit the data may bedetermined from the link characteristic information maintained by ISRs912 and 914.

FIG. 10 depicts a flow diagram of the operation performed in providing areliability of communication between supernodes in accordance with oneillustrative embodiment. As the operation begins, a transceiver, such astransceiver 908 of FIG. 9, of a processor chip receives data fromanother processor chip over a communication link (step 1002). The ISRassociated with the received processor chip retains the characteristicinformation of the particular one of communication links on which thetransceiver receives information from the other processor chip (step1004). The ISR analyzes the characteristic information associated witheach communication link in order to ascertain the reliability of eachcommunication link (step 1006). Using the analyzed information, the ISRdetermines if a threshold has been exceeded (1008). If at step 1008 apredetermined threshold has not been exceeded, then the ISR determinesif there are more communication links to analyze (step 1010). If at step1010 the ISR determines there are more communication links to analyze,the operation returns to step 1006. If at step 1010 the ISR determinesthere are no more communication links to analyze, the operationterminates.

If at step 1008 a threshold has been exceeded, then the ISR determinesif the error information associated with the communication link iscomprised of only 1's or 0's (step 1012). If at step 1012 the errorinformation is not comprised of only 1's or 0's, then the ISR indicatesthe communication link as error prone (step 1014). If at step 1012 theerror information is comprised of only 1's or 0's, the ISR indicates thecommunication link as permanently failed (step 1016). From steps 1014and 1016, the ISR transmits the communication link indicationinformation to the processor chips associated with the indicatedcommunication link (step 1018), with the operation proceeding to step1010 thereafter.

Thus, in addition to identifying individual links between processorchips that may be in a state where they are unusable, the ISR of theprocessor chip may select which set of links over which to communicatethe information based on routing table data structures and the like.While the ISR utilizes routing table data structures to select theparticular link to utilize in routing the information to the nextprocessor chip in order to get the information to an intended recipientprocessor chip, the particular link that is used to transmit the datamay be determined from the link characteristic information maintained bythe ISR.

FIG. 11A depicts an exemplary method of ISRs utilizing routinginformation to route data through a multi-tiered full-graph interconnectarchitecture network in accordance with one illustrative embodiment. Inthe example, routing of information through a multi-tiered full-graph(MTFG) interconnect architecture, such as MTFG interconnect architecture500 of FIG. 5, may be performed by each ISR of each processor chip on ahop-by-hop basis as the data is transmitted from one processor chip tothe next in a selected communication path from a source processor chipto a target recipient processor chip. As shown in FIG. 11A, and similarto the depiction in FIG. 5, MTFG interconnect architecture 1102 includessupernodes (SNs) 1104, 1106, and 1108, processor books (BKs) 1110-1120,and processor chips (PCs) 1122-1144. In order to route information fromPC 1122 to PC 1144 in MTFG interconnect architecture 1102, the ISRs mayuse a three-tiered routing table data structure topology. While thisexample uses a three-tiered routing table data structure topology, theillustrative embodiments recognize that other numbers of table datastructures may be used to route information from one processor chip toanother processor chip in MTFG interconnect architecture 1102 withoutdeparting from the spirit and scope of the present invention. The numberof table data structures may be dependent upon the particular number oftiers in the architecture.

The three-tiered routing data structure topology of the illustrativeembodiments includes a supernode (SN) routing table data structure whichis used to route data out of a source sup emode to a destinationsupernode, a book routing table data structure which is used to routedata from one processor book to another within the same supernode, and achip routing table data structure which is used to route data from onechip to another within the same processor book. It should be appreciatedthat a version of the three tiered data structure may be maintained byeach ISR of each processor chip in the MTFG interconnect architecturenetwork with each copy of the three tiered data structure being specificto that particular processor chip's position within the MTFGinterconnect architecture network. Alternatively, the three tiered datastructure may be a single data structure that is maintained in acentralized manner and which is accessible by each of the ISRs whenperforming routing. In this latter case, it may be necessary to indexentries in the centralized three-tiered routing data structure by aprocessor chip identifier, such as a SPC_ID as discussed hereafter, inorder to access an appropriate set of entries for the particularprocessor chip.

In the example shown in FIG. 11A, a host fabric interface (HFI) (notshown) of a source processor chip, such as HFI 338 in FIG. 3, providesan address 1146 of where the information is to be transmitted, whichincludes supernode identifier (SN_ID) 1148, processor book identifier(BK_ID) 1150, destination processor chip identifier (DPC_ID) 1152, andsource processor chip identifier (SPC_ID) 1154. The transmission ofinformation may originate from software executing on a core of thesource processor chip. The executing software identifies the request fortransmission of information that needs to be transmitted to a taskexecuting on a particular chip in the system. The executing softwareidentifies this information when a set of tasks that constitute acommunicating parallel “job” are spawned on the system, as each taskprovides information that lets the software and eventually HFI 338determine on which chip every other task is executing. The entire systemfollows a numbering scheme that is predetermined, such as being definedin hardware. For example, given a chip number X ranging from 0 to 65535,there is a predetermined rule to determine the supernode, the book, andthe specific chip within the book that X corresponds to. Therefore, oncesoftware informs HFI 338 to transmit the information to chip number24356, HFI 338 decomposes chip 24356 into the correct supernode, book,and chip-within-book using a rule. The rule may be as simple as:SN=floor (X/128); BOOK=floor ((X modulo 128)/16); and CHIP-WITHIN-BOOK=Xmodulo 8. Address 1146 may be provided in the header information of thedata that is to be transmitted so that subsequent ISRs along the pathfrom the source processor chip to the destination processor chip mayutilize the address in determining how to route the data. For example,portions of address 1146 may be used to compare to routing table datastructures maintained in each of the ISRs to determine the next linkover which data is to be transmitted.

It should be appreciated that SPC_ID 1154 is not needed for routing thedata to the destination processor chip, as illustrated hereafter, sinceeach of the processor chip's routing table data structures are indexedby destination identifiers and thus, all entries would have the sameSPC_ID 1154 for the particular processor chip with which the table datastructure is associated. However, in the case of a centralized threetiered routing table data structure, SPC_ID 1154 may be necessary toidentify the particular subset of entries used for a particular sourceprocessor chip. In either case, whether SPC_ID 1154 is used for routingor not, SPC_ID 1154 is included in the address in order for thedestination processor chip to know where responses should be directedwhen or after processing the received data from the source processorchip.

In routing data from a source processor chip to a destination processorchip, each ISR of each processor chip that receives the data fortransmission uses a portion of address 1146 to access its own, or acentralized, three-tiered routing data structure to identify a path forthe data to take. In performing such routing, the ISR of the processorchip first looks to SN_ID 1148 of the destination address to determineif SN_ID 1148 matches the SN_ID of the current supernode in which theprocessor chip is present. The ISR receives the SN_ID of its associatedsupernode at startup time from the software executing on the processorchip associated with the ISR, so that the ISR may use the SN_ID forrouting purposes. If SN_ID 1148 matches the SN_ID of the supernode ofthe processor chip that is processing the data, then the destinationprocessor chip is within the current supernode, and so the ISR of thatprocessor chip compares BK_ID 1150 in address 1146 to the BK_ID of theprocessor book associated with the present processor chip processing thedata. If BK_ID 1150 in address 1146 matches the BK_ID associated withthe present processor chip, then the processor chip checks DPC_ID 1152to determine if DPC_ID 1152 matches the processor chip identifier of thepresent processor chip processing the data. If there is a match, the ISRsupplies the data through the HFI associated with the processor chipDPC_ID, which processes the data.

If at any of these checks, the respective ID does not match thecorresponding ID associated with the present processor chip that isprocessing the data, then an appropriate lookup in a tier of thethree-tiered routing table data structure is performed. Thus, forexample, if SN_ID 1148 in address 1146 does not match the SN_ID of thepresent processor chip, then a lookup is performed in supernode routingtable data structure 1156 based on SN_ID 1148 to identify a pathway forrouting the data out of the present supernode and to the destinationsupernode, such as via a pathway comprising a particular set of ZLZD-buscommunication links.

If SN_ID 1148 matches the SN_ID of the present processor chip, but BK_ID1150 does not match the BK_ID of the present processor chip, then alookup operation is performed in processor book routing table datastructure 1160 based on BK_ID 1150 in address 1146. This lookup returnsa pathway within a supernode for routing the data to a destinationprocessor book. This pathway may comprise, for example, a set of Z-busand L-bus links for transmitting the data to the appropriate processorbook.

If both SN_ID 1148 and BK_ID 1150 match the respective IDs of thepresent processor chip, then the destination processor chip is withinthe same processor book as the present processor chip. If DPC_ID 1152does not match the processor chip identifier of the present processorchip, then the destination processor chip is a different processor chipwith in the same processor book. As a result, a lookup operation isperformed using processor chip routing table data structure 1162 basedon DPC_ID 1152 in address 1146. The result is a Z-bus link over whichthe data should be transmitted to reach the destination processor chip.

FIG. 11A illustrates exemplary supernode (SN) routing table datastructure 1156, processor book routing table data structure 1160, andprocessor chip routing table data structure 1162 for the portions of thepath where these particular data structures are utilized to perform alookup operation for routing data to a destination processor chip. Thus,for example, SN routing table data structure 1156 is associated withprocessor chip 1122, processor book routing table data structure 1160 isassociated with processor chip 1130, and processor chip routing tabledata structure 1162 is associated with processor chip 1134. It should beappreciated that in one illustrative embodiment, each of the ISRs ofthese processor chips would have a copy of all three types of routingtable data structures, specific to the processor chip's location in theMTFG interconnect architecture network, however, not all of theprocessor chips will require a lookup operation in each of these datastructures in order to forward the data along the path from sourceprocessor chip 1122 to destination processor chip 1136.

As with the example in FIGS. 4A and 4B, in a MTFG interconnectarchitecture that contains a large number of buses connectingsupernodes, e.g., 512 D-buses, supernode (SN) routing table datastructures 1156 would include a large number of entries, e.g., 512entries for the example of FIGS. 4A and 4B. The number of options forthe transmission of information from, for example, processor chip 1122to SN 1106 depends on the number of connections between processor chip1122 to SN 1106. Thus, for a particular SN_ID 1148 in SN routing tabledata structure 1156, there may be multiple entries specifying differentdirect paths for reaching supernode 1106 corresponding to SN_ID 1148.Various types of logic may be used to determine which of the entries touse in routing data to supernode 1106. When there are multiple directpaths from supernode 1104 to supernode 1106, logic may take into accountfactors when selecting a particular entry/route from SN routing tabledata structure 1156, such as the ECC and CRC error rate informationobtained as previously described, traffic levels, etc. Any suitableselection criteria may be used to select which entry in SN routing tabledata structure 1156 is to be used with a particular SN_ID 1148.

In a fully provisioned MTFG interconnect architecture system, there willbe one path for the direct transmission of information from a processorchip to a specific SN. With SN_ID 1148, the ISR may select the directroute or any indirect route to transmit the information to the desiredlocation using SN routing table data structure 1156. The ISR may use anynumber of ways to choose between the available routes, such as randomselection, adaptive real-time selection, round-robin selection, or theISR may use a route that is specified within the initial request toroute the information. The particular mechanism used for selecting aroute may be specified in logic provided as hardware, software, or anycombination of hardware and software used to implement the ISR.

In this example, the ISR of processor chip 1122 selects route 1158 fromsupernode route table data structure 1156, which will route theinformation from processor chip 1122 to processor chip 1130. In routingthe information from processor chip 1122 to processor chip 1130, the ISRof processor chip 1122 may append the selected supernode pathinformation to the data packets being transmitted to thereby identifythe path that the data is to take through supernode 1104. Eachsubsequent processor chip in supernode 1104 may see that SN_ID 1148 forthe destination processor chip does not match its own SN_ID and that thesupernode path field of the header information is populated with aselected path. As a result, the processor chips know that the data isbeing routed out of current supernode 1104 and may look to a supernodecounter maintained in the header information to determine the currenthop within supernode 1104.

For example, in the depicted supernode 1104, there are 4 hops fromprocessor chip 1122 to processor chip 1130. The supernode pathinformation similarly has 4 hops represented as ZLZD values. Thesupernode counter may be incremented with each hop such that processorchip 1124 knows based on the supernode counter value that it is thesecond hop along the supernode path specified in the header information.As a result, it can retrieve the next hop from the supernode pathinformation in the header and forward the data along this next link inthe path. In this way, once source processor chip 1122 sets thesupernode path information in the header, the other processor chipswithin the same supernode need not perform a SN routing table datastructure 1156 lookup operation. This increases the speed at which thedata is routed out of source supernode 1104.

When the data packets reach processor chip 1130 after being routed outof supernode 1104 along the D-bus link to processor chip 1130, the ISRof processor chip 1130 performs a comparison of SN_ID 1148 in address1146 with its own SN_ID and, in this example, determines that theymatch. As a result, the ISR of the processor chip 1130 does not look tothe supernode path information but instead looks to a processor bookpath information field to determine if a processor book path has beenpreviously selected for use in routing data through the processor bookof processor chip 1130.

In the present case, processor chip 1130 is the first processor in theprocessor book 1114 to receive the data and thus, a processor book pathhas not already been selected. Thus, processor chip 1130 performs acomparison of BK_ID 1150 from address 1146 with its own BK_ID. In thedepicted example, BK_ID 1150 will not match the BK_ID of processor chip1130 since the data is not destined for a processor chip in the sameprocessor book as processor chip 1130. As a result, the ISR of processorchip 1130 performs a lookup operation in its own processor book routingtable data structure 1160 to identify and select a ZL path to route thedata out of the present processor book to the destination processorbook. This ZL path information may then be added to the processor bookpath field of the header information such that subsequent processorchips in the same processor book will not need to perform the lookupoperation and may simply route the data along the already selected ZLpath. In this example, it is not necessary to use a processor bookcounter since there are only two hops, however in other architectures itmay be necessary or desirable to utilize a processor book countersimilar to that of the supernode counter to monitor the hops along thepath out of the present processor book. In this way, processor chip 1130determines the route that will get the information/data packets fromprocessor chip 1130 in processor book 1114 to processor book 1116.

Processor book routing table data structure 1160 includes routinginformation for every processor chip in processor book 1114 to everyother processor book within the same supernode 1106. Processor bookrouting table data structure 1160 may be generic, in that the positionof each processor chip to every other processor chip within a processorbook and each processor book to every other processor book in asupernode is known by the ISRs. Thus, processor book route table 1160may be generically used within each supernode based on the position ofthe processor chips and processor books, rather to specific identifiersas used in this example.

As with the example in FIGS. 4A and 4B, in a MTFG interconnectarchitecture that contains 16 L-buses per book, processor book routingtable data structure 1160 would include 16 entries. Thus, processor bookrouting table data structure 1160 would include only one option for thetransmission of information from processor chip 1130 to processor book1116. However, depending on the number of virtual channels that areavailable, the ISR may also have a number of indirect paths from whichto choose at the L-bus level. While the previously described exemplarypseudocode provides for only one indirect route using only one of theZ-buses, L-buses, or D-buses, other routing algorithms may be used thatprovides for multiple indirect routing using one or more Z-buses,L-buses, and D-buses. When processor chip 1134 receives theinformation/data packets, the ISR of the processor chip 1134 checksSN_ID 1148 of address 1146 and determines that SN_ID 1148 matches itsown associated SN_ID. The ISR of processor chip 1134 then checks BK_ID1150 in address 1146 and determines that BK_ID 1150 matches its ownassociated BK_ID. Thus, the information/data packets are destined for aprocessor chip in the same supernode 1106 and processor book 1116 asprocessor chip 1134. As a result, the ISR of processor chip 1134 checksDPC_ID 1152 of address 1146 against its own processor chip identifierand determines that the two do not match. As a result, the ISR ofprocessor chip 1134 performs a lookup operation in processor chiprouting table data structure 1162 using DPC_ID 1152. The resulting Zpath is then used by the ISR to route the information/data packets tothe destination processor chip 1136.

Processor chip routing table data structure 1162 includes routing forevery processor chip to every other processor chip within the sameprocessor book. As with processor book route table data structure 1160,processor chip routing table data structure 1162 may also be generic, inthat the position of each processor chip to every other processor chipwithin a processor book is known by the ISRs. Thus, processor chiprouting table data structure 1162 may be generically used within eachprocessor book based on the position of the processor chips, as opposedto specific identifiers as used in this example.

As with the example in FIGS. 4A and 4B, in a MTFG interconnectarchitecture that contains 7 Z-buses, processor chip routing table datastructure 1162 would include 8 entries. Thus, processor chip routingtable data structure 1162 would include only one option for thetransmission of information from processor chip 1134 to processor chip1136. Alternatively, in lieu of the single direct Z path, the ISR maychoose to use indirect routing at the Z level. Of course, the ISR willdo so only if the number of virtual channels are sufficient to avoid thepossibility of deadlock. In certain circumstances, a direct path fromone supernode to another supernode may not be available. This may bebecause all direct D-buses are busy, incapacitated, or the like, makingit necessary for an ISR to determine an indirect path to get theinformation/data packets from SN 1104 to SN 1106. For instance, the ISRof processor chip 1122 could detect that a direct path is temporarilybusy because the particular virtual channel that it must use tocommunicate on the direct route has no free buffers into which data canbe inserted. Alternatively, the ISR of processor chip 1122 may alsochoose to send information over indirect paths so as to increase thebandwidth available for communication between any two end points. Aswith the above example, the HFI of the source processor provides theaddress of where the information is to be transmitted, which includessupernode identifier (SN_ID) 1148, processor book identifier (BK_ID)1150, destination processor chip identifier (DPC_ID) 1152, and sourceprocessor chip identifier (SPC_ID) 1154. Again, the ISR uses the SN_ID1148 to reference the supernode routing table data structure 1156 todetermine a route that will get the information from processor chip 1122to supernode (SN) 1106.

However, in this instance the ISR may determine that no direct routesare available, or even if available, should be used (due to, forexample, traffic reasons or the like). In this instance, the ISR woulddetermine if a path through another supernode, such as supernode 1108,is available. For example, the ISR of processor chip 1122 may selectroute 1164 from supernode routing table data structure 1156, which willroute the information from processor chips 1122, 1124, and 1126 toprocessor chip 1138. The routing through supernode 1104 to processorchip 1138 in supernode 1108 may be performed in a similar manner asdescribed previously with regard to the direct route to supernode 1106.When the information/data packets are received in processor chip 1138, asimilar operation is performed where the ISR of processor chip 1138selects a path from its own supernode routing table data structure toroute the information/data from processor chip 1138 to processor chip1130. The routing is then performed in a similar way as previouslydescribed between processor chip 1122 and processor chip 1130.

The choice to use a direct route or indirect route may be softwaredetermined, hardware determined, or provided by an administrator.Additionally, the user may provide the exact route or may merely specifydirect or indirect, and the ISR of the processor chip would select fromthe direct or indirect routes based on such a user defined designation.It should be appreciated that it is desirable to minimize the number oftimes an indirect route is used to arrive at a destination processorchip, or its length, so as to minimize latency due to indirect routing.Thus, there may be an identifier added to header information of the datapackets identifying whether an indirect path has been already used inrouting the data packets to their destination processor chip. Forexample, the ISR of the originating processor chip 1122 may set thisidentifier in response to the ISR selecting an indirect routing option.Thereafter, when an ISR of a processor chip is determining whether touse a direct or indirect route to transmit data to another supernode,the setting of this field in the header information may cause the ISR toonly consider direct routes.

Alternatively, this field may constitute a counter which is incrementedeach time an ISR in a supernode selects an indirect route fortransmitting the data out of the supernode. This counter may be comparedto a threshold that limits the number of indirect routes that may betaken to arrive at the destination processor chip, so as to avoidexhausting the number of virtual channels that have been pre-allocatedon the path.

FIG. 11B is a flowchart outlining an exemplary operation for selecting aroute based on whether or not the data has been previously routedthrough an indirect route to the current processor, in accordance withone illustrative embodiment. The operation outlined in FIG. 11B may beperformed, for example, within a ISR of a processor chip, either usinghardware, software, or any combination of hardware and software withinthe ISR. It should be noted that in the following discussion of FIG.11B, “indirect” and “direct” are used in regard to the D-buses, i.e.buses between supernodes.

As shown in FIG. 11B, the operation starts with receiving data havingheader information with an indirect route identifier and an optionalindirect route counter (step 1182). The header information is read (step1184) and a determination is made as to whether the indirect routeidentifier is set (step 1186). As mentioned above, this identifier mayin fact be a counter in which case it can be determined in step 1186whether the counter has a value greater than 0 indicating that the datahas been routed through at least one indirect route.

If the indirect route identifier is set, then a next route for the datais selected based on the indirect route identifier being set (step1188). If the indirect route identifier is not set, then the next routefor the data is selected based on the indirect route being not set (step1192). The data is then transmitted along the next route (step 1190) andthe operation terminates. It should be appreciated that the aboveoperation may be performed at each processor chip along the pathway tothe destination processor chip, or at least in the first processor chipencountered in each processor book and/or supernode along the pathway.

In step 1188 certain candidate routes or pathways may be identified bythe ISR for transmitting the data to the destination processor chipwhich may include both direct and indirect routes. Certain ones of theseroutes or pathways may be excluded from consideration based on theindirect route identifier being set. For example, the logic in the ISRmay specify that if the data has already been routed through an indirectroute or pathway, then only direct routes or pathways may be selectedfor further forwarding of the data to its destination processor chip.Alternatively, if an indirect route counter is utilized, the logic maydetermine if a threshold number of indirect routes have been utilized,such as by comparing the counter value to a predetermined threshold, andif so, only direct routes may be selected for further forwarding of thedata to its destination processor chip. If the counter value does notmeet or exceed that threshold, then either direct or indirect routes maybe selected.

Thus, the benefits of using a three-tiered routing table data structuretopology is that only one 512 entry supernode route table, one 16 entrybook table, and one 8 entry chip table lookup operation are required toroute information across a MTFG interconnect architecture. Although theillustrated table data structures are specific to the depicted example,the processor book routing table data structure and the processor chiprouting table data structure may be generic to every group of books in asupernode and group of processor chips in a processor book. The use ofthe three-tiered routing table data structure topology is an improvementover known systems that use only one table and thus would have to have arouting table data structure that consists of 65,535 entries to routeinformation for a MTFG interconnect architecture, such as the MTFGinterconnect architecture shown in FIGS. 4A and 4B, and which would haveto be searched at each hop along the path from a source processor chipto a destination processor chip. Needless to say, in a MTFG interconnectarchitecture that consists of different levels, routing will beaccomplished through correspondingly different numbers of tables.

FIG. 12 depicts a flow diagram of the operation performed to route datathrough a multi-tiered full-graph interconnect architecture network inaccordance with one illustrative embodiment. In the flow diagram therouting of information through a multi-tiered full-graph (MTFG)interconnect architecture may be performed by each ISR of each processorchip on a hop-by-hop basis as the data is transmitted from one processorchip to the next in a selected communication path from a sourceprocessor chip to a target recipient processor chip. As the operationbegins, an ISR receives data that includes address information for adestination processor chip (PC) from a host fabric interface (HFI), suchas HFI 338 in FIG. 3 (step 1202). The data provided by the HFI includesan address of where the information is to be transmitted, which includesa supernode identifier (SN_ID), a processor book identifier (BK_ID), adestination processor chip identifier (DPC_ID), and a source processorchip identifier (SPC_ID). The ISR of the PC first looks to the SN_ID ofthe destination address to determine if the SN_ID matches the SN_ID ofthe current supernode in which the source processor chip is present(step 1204). If at step 1204 the SN_ID matches the SN_ID of thesupernode of the source processor chip that is processing the data, thenthe ISR of that processor chip compares the BK_ID in the address to theBK_ID of the processor book associated with the source processor chipprocessing the data (step 1206). If at step 1206 the BK_ID in theaddress matches the BK_ID associated with the source processor chip,then the processor chip checks the DPC_ID to determine if the DPC_IDmatches the processor chip identifier of the source processor chipprocessing the data (step 1208). If at step 1208 there is a match, thenthe source processor chip processes the data (step 1210), with theoperation ending thereafter.

If at step 1204 the SN_ID fails to match the SN_ID of the supernode ofthe source processor chip that is processing the data, then the ISRreferences a sup emode routing table to determine a pathway to route thedata out of the present supernode to the destination supernode (step1212). Likewise, if at step 1206 the BK_ID in the address fails to matchthe BK_ID associated with the source processor chip, then the ISRreferences a processor book routing table data structure to determine apathway within a supernode for routing the data to a destinationprocessor book (step 1214). Likewise, if at step 1208 the DPC_ID failsto match the SPC_ID of the source processor chip, then the ISR referencea processor chip routing table data structure to determine a pathway toroute the data from the source processor chip to the destinationprocessor chip (step 1216).

From steps 1212, 1214, or 1216, once the pathway to route the data fromthe source processor chip to the respective supernode, book, orprocessor chip is determined, the ISR transmits the data to a currentprocessor chip along the identified pathway (step 1218). Once the ISRcompletes the transmission, the ISR where the data now residesdetermines if the data has reached the destination processor chip bycomparing the current processor chip's identifier to the DPC_ID in theaddress of the data (step 1220). If at step 1220 the data has notreached the destination processor chip, then the ISR of the currentprocessor chip where the data resides, continues the routing of the datawith the current processor chip's identifier used as the SPC_ID (step1222), with the operation proceeding to step 1204 thereafter. If at step1220 the data has reached the destination processor chip, then theoperation proceeds to step 1210.

Thus, using a three-tiered routing table data structure topology thatcomprises only one 512 entry supernode route table, one 16 entry booktable, and one 8 entry chip table lookup to route information across aMTFG interconnect architecture improves over known systems that use onlyone table that consists of 65,535 entries to route information.

FIG. 13 depicts an exemplary supernode routing table data structure thatsupports dynamic selection of routing within a multi-tiered full-graphinterconnect architecture using no-direct and no-indirect fields inaccordance with one illustrative embodiment. In addition to the exampledescribed in FIG. 9, where one or more optical fibers or wires for aport may be unavailable and, thus, the port may perform at a reducedcapacity, there may also be instances where for one or more of the portsor the entire bus, either Z-bus, D-bus, or L-bus, may not be available.Again, this may be due to instances during manufacturing, shipping,usage, adjustment, or the like, where the one or more optical fibers orwires may end up broken or otherwise unusable. In such an event, thesupernode (SN) routing table data structure, the processor book routingtable data structure, and the processor chip routing table datastructure, such as SN routing table data structure 1156, processor bookrouting table data structure 1160, and processor chip routing table datastructure 1162 of FIG. 11A, may require updating so that an ISR, such asintegrated switch/router 338 of FIG. 3, will not use a route thatincludes the broken or unusable bus.

For example, SN routing table data structure 1302 may include fieldsthat indicate if the specific route may be used as a direct or anindirect route. No direct route (NDR) indicator 1304 and no indirectroute (NIDR) indicator 1306 may be used by the ISR in selecting anappropriate route to route information through the multi-tieredfull-graph (MTFG) interconnect architecture network. NDR indicator 1304may be used to specify whether a particular direct route from a givenchip to a specific SN is available. For instance, if any of the linkscomprising the route entry 1308 are unavailable, or there is asignificant enough degradation in availability of links, then thecorresponding NDR indicator 1304 entry may be set.

The NIDR indicator 1306 entry indicates whether a particular path may beused for indirect routing of information/data packets. This NIDRindicator 1306 may be set in response to a link in the path becomingunavailable or there is a significant enough degradation in availabilityof the links, for example. In general, if a pathway cannot be used fordirect routing, it will generally not be available for indirect routing.However, there are some cases where a path may be used for directrouting and not for indirect routing. For example, if the availabilityof a link in the path is degraded, but not made completely unavailable,the path may be permitted to be used for direct routing but not indirectrouting. This is because the additional latency due to the degradedavailability may not be so significant as to make the path unusable fordirect routing but it would create too much latency in an indirect pathwhich already incurs additional latency by virtue of it being anindirect routing. Thus, it is possible that the bits in NIDR indicator1306 may be set while the bits in the NDR indicator 1304 are not set.

The NIDR indicator 1306 may also come into use because of a determinedlongest route that can be taken in the multi-tiered hierarchicalinterconnect. Consider an indirect path from processor chip 1122 toprocessor chip 1136 in FIG. 11A that consists of the following hops:1122→1124→1126→1128→1138→1140→1142→1144→1130→1132→1134→1136. If the partof the route from SN 1108 to SN 1106 is not available, such as the hop1140→1142, then processor chip 1122 needs to know this fact, which, forexample, is indicated by indicator 1312 in NIDR indicator 1306 field.Processor chip 1122 benefits from knowing this fact because of potentiallimitations in the number of virtual channels that are available causinga packet destined for SN 1106 that is routed to SN 1108 to only berouted over the single direct route from SN 1108 to SN 1106.Consequently, if any direct route from SN 1108 to any other SN is notavailable, then the entries in all the SN routing table data structuresthat end in supernode 1108 will have the corresponding NIDR indicator1306 field set.

NIDR indicator 1306 may also be set up to contain more than one bit. Forinstance, NIDR indicator 1306 may contain multiple bits where each bitpertains to a specific set of direct routes from the destination SNidentifier field, such as SN_ID 1148 of FIG. 11A, to all other SNs.

In order to determine if a specific route is not available, the ISR mayattempt to transmit information over the route a number of predeterminedtimes. The ISR may increment a counter each time a packet of informationis dropped. Based on the value of the counter meeting a predeterminedvalue, the ISR may set either or both of NDR indicator 1304 or NIDRindicator 1306 fields to a value that indicates the specific route isnot to be used as a path for transmitting information. The predeterminedvalue may be determined by an administrator, a preset value, or thelike. NIDR indicator 1306 may also be set by an external software entitysuch as network management software.

In determining if a route is not available, the ISR may narrow a largerpath, such as those in route 1314, to determine the specific bus that isbroken. For example, in route 1308 there may only be one bus of the fourbuses in the route that is broken. Once the ISR determines the specificbroken bus, such as exemplary bus 1310, the ISR may update NDR indicator1304 or NIDR indicator 1306 fields for each route in supernode routingtable data structure 1302 to indicate that each route that includes thespecific bus may not be used for a direct or indirect path. In thiscase, the ISR may also update route 1316 as it also includes bus 1310.Although not depicted, the ISR may update similar fields in theprocessor book routing table and processor chip routing table datastructures to indicate that each route that includes the specific busmay not be used for a direct or indirect path.

Thus, using NDR indicator 1304 or NIDR indicator 1306 fields inconjunction with supernode routing table data structure 1302 providesfor a more efficient use of the three-tier route table topology based ondetected broken or unusable communication connections. That is, usingNDR indicator 1304 or NIDR indicator 1306 fields ensures that onlyfunctioning routes in the MTFG interconnect architecture network areused, thereby improving the performance of the ISRs and theinformation/data packet routing operations.

FIG. 14A depicts a flow diagram of the operation performed in supportingthe dynamic selection of routing within a multi-tiered full-graphinterconnect architecture using no-direct and no-indirect fields inaccordance with one illustrative embodiment. As the operation begins, anISR attempts to transmit information over a route (step 1402). The ISRdetermines if any packet of information is dropped during thetransmission of the data (step 1404). If at step 1404 no data packet hasbeen dropped, the operation returns to step 1402. If at step 1404 a datapacket has been dropped during the transmission of data, the ISRincrements a value of a counter for the particular route (step 1406).The ISR then determines if the value of the counter meets or exceeds apredetermined value (step 1408). If at step 1408 the value of thecounter has not met or exceeded the predetermined value, then theoperation returns to step 1402. If at step 1408 the value of the counterhas met or exceeded the predetermined value, the ISR sets either or bothof the NDR indicator or the NIDR indicator fields to a value thatindicates the specific route is not to be used as a path fortransmitting information (step 1410), with the operation returning tostep 1402 thereafter. Furthermore, the ISR may inform other ISRs in thesystem to amend their routing tables or may inform network managementsoftware which may in turn inform other ISRs to amend their routingtables.

Thus, using the NDR indicator or NIDR indicator fields in conjunctionwith a supernode routing table data structure provides for a moreefficient use of the three-tiered routing table data structure topologybased on detected broken or unusable communication connections.

FIG. 14B outlines an exemplary operation for selecting a route fortransmitting data based on whether or not a no-direct or no-indirectindicator is set in accordance with one illustrative embodiment. Theoperation outlined in FIG. 14B may be performed, for example, within anISR of a processor chip, either using hardware, software, or anycombination of hardware and software within the ISR.

As shown in FIG. 14B, the operation starts with receiving data havingdirected to a destination processor chip (step 1420). The addressinformation in the header information of the data is read (step 1422)and based on the address information, candidate routes for routing thedata to the destination processor chip are selected from one or morerouting table data structures (step 1424). For each indirect route inthe selected candidates, the entries in the one or more routing tabledata structures are analyzed to determine if their “no-indirect”identifiers are set (step 1426). If an indirect route has an entryhaving the “no-indirect” identifier set (step 1428), then that indirectroute is eliminated as a candidate for routing the data (step 1430).

For each of the direct routes in the selected candidates, the entries inthe one or more routing table data structures are analyzed to determineif their “no-direct” identifiers are set (step 1432). If a direct routehas an entry having the “no-direct” identifier set (step 1434), thenthat direct route is eliminated as a candidate for routing the data(step 1436). The result is a set of candidate routes in which the routesare permitted to be utilized in the manner necessary to route data fromthe current processor to the destination processor, i.e. able to be usedas indirect or direct routes.

From the resulting subset of candidate routes, a route for transmittingthe data to the destination processor chip is selected (step 1438). Thedata is then transmitted along the selected route toward the destinationprocessor chip (step 1440). The operation then terminates. It should beappreciated that the above operation may be performed at each processorchip along the pathway to the destination processor chip, or at least inthe first processor chip encountered in each processor book and/orsupernode along the pathway.

Having described the multi-tiered full graph (MTFG) interconnectarchitecture and the mechanisms for routing data communications or datatransmissions through the architecture from one processor chip toanother, in the same or different processor book on the same ordifferent supernode, it can be appreciated that the architecture lendsitself to various types of multiprocessor processing applications thatmay utilize a large number of processors, or cores, to execute largescale applications. For example, one possible use of the MTFGinterconnect architecture is to perform synchronized processing ofdistributed jobs across a plurality of processors on the same ordifferent processor chips in the same or different processors books onthe same or different supernodes. The plurality of processors, processorbooks, and supernodes may constitute a computing cluster for purposes ofperforming synchronized processing of distributed jobs. One processor orprocessor chip in the computing cluster may act as the coordinator ofthe computing cluster such that it handles orchestration of the overalloperation of the computing cluster.

Synchronized operation of two or more supernodes may be desirable inmany different applications. For example, synchronized operation may bedesirable to address operating system jitter, i.e. mismatch inscheduling of tasks and interrupts, to tune and debug applications, andto trigger performance counters.

As mentioned above, typically in a computing cluster, the variouscomputing devices, which may provide one or more processors each for usein the computing cluster, operate using their own internal system clockthat is not synchronized with the system clocks of the other computingdevices in the computing cluster. Thus, other mechanisms, typicallyimplemented in software, must be provided for handling thesynchronization of the performance of jobs by each of the processors ofeach of the computing devices. Moreover, since the system clocks are notsynchronized, often jobs may be completed in one computing device fasterthan in other computing devices and, as a result, a period of idlenessand wasted processing cycles is experienced.

The illustrative embodiments aid in reducing this additionalsynchronization overhead and loss of processing efficiency by providingan automated mechanism for synchronizing system clocks in all processorsof a computing cluster, thereby providing a cluster-wide system clock.In this way, each processor is synchronized with each other processor inthe computing cluster and, as a result, wasted processing cycles may bereduced.

In particular, the illustrative embodiments provide a system and methodfor providing a cluster-wide system clock in a multi-tiered full graph(MTFG) interconnect architecture. With the system and method of theillustrative embodiments, the MTFG interconnect architecture isconfigured as discussed above using supernodes, processor books, andprocessor chips with the above-described routing mechanisms also beingprovided for routing data between processor chips in the same processorbook, in a different processor book of a same supernode, and in adifferent processor book of a different supernode of the MTFGinterconnect architecture. Moreover, as discussed above the various Z,L, and D buses are provided between the processor chips, the processorbooks, and the supernodes, respectively, for transmission of databetween the various elements of the MTFG interconnect architecture.

In one illustrative embodiment, the multi-tiered architecture, andoptionally the routing mechanisms, may be utilized for routing aheartbeat signal to each of the processor chips within a definedcomputing cluster from each of the other processor chips directlycoupled to the processor chip. A heartbeat signal is a small size datacommunication that is sent out at a regular interval to each of theother processor chips with which a current processor chip has directconnection through ports or phys of the processor chip and a bus. Theheartbeat signal, in one illustrative embodiment, is used simply as amechanism for identifying that the source of the heartbeat signal isstill operational. The heartbeat signal may have no useable data in itor may have some small amount of data, such as header informationidentifying the SN_ID, BK_ID, DPC_ID, or the like, of the source of theheartbeat signal. The key concept being that the signal is a small sizedata communication being sent at a regular, and thus predictable, timeinterval.

This heartbeat signal may be used by the processor chips to identifyother processor chips that are directly coupled to them that may be in afailed state, whose connections may be in a failed state, or the like.Each processor chip may contain logic for identifying heartbeat signalsfrom neighboring processor chips, i.e. processor chips that have adirect connection with the current processor chip through a single buswithout having to be redirected through another processor chip. If aparticular neighboring processor chip does not provide a heartbeatsignal within a predetermined period of time of a previously receivedheartbeat signal from that processor chip, then it may be determinedthat the neighboring processor chip that has not sent its heartbeatsignal is in an error or failed state.

As a result of identifying a processor chip as being in an error orfailed state, the processor chip detecting the error or failed state mayupdate its corresponding routing table data structures accordingly. Forexample, based on an identifier of the error or failed state processorchip, i.e. its SN_ID, BK_ID, and DPC_ID, the ISR of the processor chipthat detected the error or failed state processor chip may identifyentries in the routing table data structures corresponding to routeshaving the error or failed state processor chip. The ISR may then updatethe entries in the routing table data structures to either eliminate theentry or otherwise mark the entry as not suitable for direct and/orindirect routing. The ISR may also communicate the error or failed stateto each of the other processor chips in the MTFG interconnectarchitecture so that they may update their associated routing table datastructures accordingly. As a result, based on the heartbeat signalsbeing exchanged between processor chips, error or failed state processorchips may be dynamically identified and routing mechanisms may bedynamically updated based on detected error or failed state processorchips.

In addition to simply identifying error or failed state processor chipsin the MTFG interconnect architecture, the illustrative embodiments mayutilize the heartbeat signal to distribute data to all of the processorchips in the MTFG interconnect architecture, or a subset of processorchips in the MTFG interconnect architecture, as well as facilitatevarious other collaborative operations within the MTFG interconnectarchitecture or a subset thereof. For example, in one illustrativeembodiment, the heartbeat signals may be utilized to provide asynchronized cluster-wide system clock for all of the processor chips inthe MTFG interconnect architecture, or a subset of the MTFG interconnectarchitecture.

In such an illustrative embodiment, each of the processor chips in theMTFG interconnect architecture, or in a subset of processor chips in theMTFG interconnect architecture, e.g., a computing cluster, may beinitially synchronized through a heartbeat synchronization process. Thisheartbeat synchronization process may involve a master processor chip,i.e. a processor chip initiating the heartbeat synchronization process.For example, the processor chip may send out a data communication toeach of the processor chips in the computing cluster, using the directand indirect routing of the data communication to all of the processorchips, that indicates that a heartbeat synchronization process is to beperformed. The ISR of the master processor chip may then identify eachof the processor chips that are directly coupled to the master processorchip, whether in the same or different processor book or in the same ordifferent supernode. The term “directly coupled” refers to processorchips that are in communication with each other via a communication linkthat couples the two processor chips without having to re-route thecommunication through a third processor chip.

The master processor chip may then distribute a heartbeat signal, i.e. asmall data communication, to each of the processor chips with which itis directly coupled, whether those processor chips be in the same book,same supernode, different book, or different supernode. The heartbeatsignal preferably includes a timestamp of when the heartbeat signal wastransmitted and may include identification information for the source ofthe heartbeat signal. This timestamp may be used by receiving processorchips to determine a delay during transmission of the heartbeat signalsuch that the processor chips may predict when the next heartbeat signalfrom the master processor chip may be transmitted.

The receiving processor chips then generate and transmit their ownheartbeat signal to their directly coupled processor chips at thepredicted time when the master processor chip sends its next heartbeatsignal. This process continues with each subsequent receiving processorchip until all of the processor chips in the computing cluster have beensynchronized based on the heartbeat signal to be transmitting theirheartbeat signals at the same time. For example, a sufficientpredetermined amount of time may be allowed to elapse, based on the sizeof the computing cluster and number of processor chips therein, topermit all of the processor chips in the computing cluster to becomesynchronized through the heartbeat signal mechanism. After thispredetermined amount of time has elapsed, the master processor chip mayagain distribute a data communication to each of the processor chips inthe computing cluster, through the direct or indirect routingmechanisms, to indicate that the heartbeat synchronization process hascompleted.

Once synchronized in this manner, each of the processor chips may usethe heartbeat signal it generates to provide an internal system clock.The system clock may be used by the processor chips in timing theprocessing of instructions with processors of the processor chips. Sincethe heartbeat signals of the processor chips are synchronized, theinternal system clocks of the processor chips are also synchronized.Thus, operations being performed on each of the processor chips in eachof the processor books of each of the supernodes in a computing clustermay have their operations or tasks synchronized to the same cluster-widesystem clock. This results in a reduction of wasted processor cycleswaiting for operations or tasks to complete on other processor chips andreduces latency in the overall computing cluster.

Even though the system clocks of the processor chips may be synchronizedin the above manner, over time the system clocks may drift out ofsynchronization due to any of a number of different factors. Thus, eachprocessor chip may monitor the receipt of heartbeat signals from itsdirectly coupled processor chips to determine if any of the processorchip heartbeat signals drift significantly. That is, a differencebetween timestamps of received heartbeat signals and a heartbeat signalbeing generated by the processor chip may be determined and compared toa threshold. If the threshold is exceeded, the above heartbeatsynchronization process may be again performed to bring the processorchips back into synchronization. It should be appreciated that theheartbeat synchronization process in the MTFG interconnect architectureshould require approximately three processor cycles to complete onceinitiated and thus, does not introduce a significant amount of overheadprocessing into the computing cluster.

It should be appreciated that the illustrative embodiments are notlimited to looking up direct routes in routing table data structures andsending the heartbeat signals along the direct routes. To the contrary,in other illustrative embodiments, the heartbeat signal may be simplybroadcast to all ports, or phys, associated with an ISR of a processorchip such that the heartbeat signal is sent to all directly coupledprocessor chips. The lookup operations described above allow theprocessor chip to identify, via the routing table data structures, thosecommunication links that are in an error state or otherwise not useable.In the alternative embodiment, the broadcast of the heartbeat signal maybe performed regardless of broken or error state links with theexpectation that because each processor chip broadcasts to each of itsdirectly coupled processor chips, that the heartbeat signal will be sendalong other communication links from other processor chips to aprocessor chip connected by way of a broken link or error state link. Ineither case, the effect is to broadcast the heartbeat signal to thedirectly coupled processor chips, if the communication link has notbecome broken or unusable, with each processor chip then sending its ownheartbeat signal to its directly coupled processor chips, and so on.

FIG. 15 is an exemplary block diagram of a simplified computing clusterin accordance with one illustrative embodiment. The computing clustershown in FIG. 15 includes only two supernodes with each supernode havingonly two of its processor books shown for simplicity. It should beappreciated that any number of supernodes, processor books, andprocessor chips within processor books may be used with the mechanismsof the illustrative embodiments without departing from the spirit andscope of the present invention. For simplicity of the explanation of theoperation of the illustrative embodiments, only one direct connectionbetween a processor chip and another processor chip in a differentprocessor book on the same supernode and a different processor book on adifferent supernode are shown. However, it should be appreciated that asame operation as will be detailed hereafter applies to all directconnections between processor chips.

As shown in FIG. 15, the computing cluster 1500 comprises a firstsupernode A 1501 and a second supernode B 1502. As mentioned above, thisis a simplified depiction for ease of explanation, however the actualcomputing cluster may comprise additional supernodes (not shown) of anynumber and may in fact comprise all of the supernodes in the MTFGinterconnect architecture, depending upon the particular implementationof the illustrative embodiments desired.

Each supernode comprises one or more processor books. For example,supernode A 1501 comprises processor books 1510 and 1520 while supernodeB 1502 comprises processor books 1530 and 1540. While only two processorbooks are shown for each of the supernodes 1501-1502, it should beappreciated that any number of processor books may be utilized withoutdeparting from the spirit and scope of the illustrative embodiments.Each processor book 1510-1540 comprises one or more processor chips witheach processor chip in a processor book being directly coupled to eachother processor chip in the processor book. Similarly each processorbook of a supernode is directly coupled to at least one processor chipof each other processor book of the same supernode. Each supernode isconnected to each other supernode in the computing cluster via at leastone processor chip.

In one illustrative embodiment, each processor chip is connected to aprocessor chip in two other processor books of the same supernode.Moreover, each supernode is connected to one processor chip of eachother supernode in the computing cluster. Thus, each processor chip (forexample, the upper right processor chip of processor book 1510) iscoupled to a single processor chip of each other processor book (forexample, the upper right processor chip of processor book 1520).Moreover, a single processor chip (the processor chip in the upper rightof processor book 1510) in supernode 1501 is directly coupled to asingle processor chip (the upper left processor chip of processor book1530) in supernode 1502.

With the computing cluster 1500 shown in FIG. 15, it is assumed that aprocessor chip, e.g., the upper right processor chip of processor book1510, determines that it is necessary to perform a heartbeatsynchronization operation. The determination of when to perform such aheartbeat synchronization operation may be made based on many differentfactors. As one example, the heartbeat synchronization operation may beinitiated in response to a user input requesting the operation to beperformed. As another example, such a determination may be made based ona type of application or job that is to be processed by the computingcluster. For example, if the application or job has an associatedindicator identifying the application or job as one that requiressynchronization of the processor chips in the computing cluster, thenthe heartbeat synchronization operation may be initiated accordingly.Moreover, as will be discussed in greater detail hereafter, theheartbeat synchronization operation may be initiated in response to adetermination that synchronization of at least two processor chips inthe computing cluster are sufficiently out of synchronization with eachother, thereby requiring a re-synchronization using the heartbeatsynchronization operation. Other factors and events may be used toinitiate the heartbeat synchronization operation as will become readilyapparent to those of ordinary skill in the art in view of the presentdescription.

Having determined that a heartbeat synchronization operation is needed,the processor chip, herein referred to as the master processor chip, maythen broadcast a message, or data communication signal, to each of theother processor chips in the computing cluster 1500 the intent toperform the heartbeat synchronization operation. The broadcasting of themessage may be performed using direct and/or indirect routing asdictated by the routing table data structures maintained by the ISR ofthe master processor chip. In response to receiving this broadcastcommunication, heartbeat synchronization logic in each of the processorchips may be initialized for performing the heartbeat synchronizationoperation, as will be described with reference to FIGS. 16-18 hereafter.

The master processor chip may keep track of an elapsed time since theheartbeat synchronization operation was initiated to determine when todiscontinue the heartbeat synchronization operation. For example, basedon the size of the computing cluster, i.e. the number of supernodes,processor books, and processor chips, a predetermined amount of time maybe established for ensuring that all of the processor chips in thecomputing cluster are synchronized using the heartbeat synchronizationoperation. The master processor chip may compare the current elapsedtime since the heartbeat synchronization operation was initiated withthis predetermined amount of time to determine if the predeterminedamount of time has been met or exceeded and, as a result, the heartbeatsynchronization operation may be terminated. In response to the masterprocessor chip determining that the heartbeat synchronization operationmay be terminated, the master processor chip may send out anotherbroadcast message to the processor chips indicating the termination ofthe heartbeat synchronization operation.

In response to receiving the termination message, the heartbeatsynchronization logic of the processor chips may exit the heartbeatsynchronization operation and may then utilize their own generatedheartbeat signals as internal system clock signals for timing theoperation of the processors, or cores, of the processor chip. Since eachof the heartbeat signals of each of the processor chips are nowsynchronized, the corresponding internal system clock signals of theprocessor chips are also synchronized. Thus, jobs or tasks beingexecuted by the processors, or cores, of the processor chips are alsosynchronized based on the system clocks. Hence, the illustrativeembodiments provide a mechanism for providing a cluster-wide systemclock through the synchronization of heartbeat signals of processorchips in a MTFG interconnect architecture.

FIGS. 16-18 show three processor cycles during a heartbeatsynchronization operation in accordance with one illustrativeembodiment. FIG. 16 shows a first processor cycle after notification toall processor chips that the heartbeat synchronization operation isbeing performed. FIG. 17 shows the next processor cycle and FIG. 18shows the next processor cycle after FIG. 17. In these figures,gray-shaded processor chips represent the processor chips which aresynchronized as a result of the distribution of heartbeat signals duringthat processor cycle. Processor chips having a dotted shading representprocessor chips that were synchronized in a previous processor cycle.Thus, FIGS. 16-18 together show the progression of synchronization fromthe master processor chip to all processor chips of the computingcluster.

Referring now to FIG. 16, an exemplary diagram illustrating a firstcycle of a heartbeat synchronization process or operation executed inthe computing cluster of FIG. 15 is depicted in accordance with oneillustrative embodiment. As shown in FIG. 16, a master processor chip1610, after sending the initiation message of the heartbeatsynchronization operation, sends out a heartbeat signal to each of theprocessor chips directly coupled to the master processor chip 1610. Thisincludes all of the processor chips 1620 in the same processor book asthe master processor chip 1610, the processor chip(s) 1630 in otherprocessor books of the same supernode A, and one processor chip 1640 ineach of the other supernodes, i.e. in this example supernode B. Theidentification of these directly coupled processor chips may beperformed by the ISR of the master processor chip 1610 using the routingtable data structures previously described above. Any entry in therouting table data structures comprising a single hop, i.e. transmissionacross a single bus whether it be Z, L, or D, to reach a destinationprocessor chip is considered to be a direct coupling of the masterprocessor chip 1610 with the destination processor chip. Alternatively,the ISR may broadcast the heartbeat signal to each of the portsassociated with the ISR such that the heartbeat signal is sent to alldirectly coupled processor chips without having to perform a lookupoperation in the routing table data structures to identify directlycoupled routes.

The processor chips 1620-1640, having been set to a heartbeatsynchronization operation state by the previous initiation messagebroadcast by the master processor chip 1610, process the heartbeatsignal from the master processor chip 1610 to determine how tosynchronize their own heartbeat signals to be transmitted atapproximately the same time as the heartbeat signal of the masterprocessor chip 1610. As mentioned previously, the heartbeat signalpreferably includes a timestamp indicating when the heartbeat signal wastransmitted by the source, in this case master processor chip 1610.Moreover, the heartbeat signal may specify a periodicity of theheartbeat signal, e.g., the regular interval at which the heartbeatsignal is transmitted. Furthermore, the frequency of the internal systemclock signals to be generated based on the heartbeat signal may bespecified in the heartbeat signal. Alternatively, the periodicity of theheartbeat signal itself may be used to control the frequency of theinternal system clock signals by timing the clock signals to besubstantially at the same time as the heartbeat signals.

The timestamp of the heartbeat signal may be compared with a time atwhich the heartbeat signal was received by the processor chips 1620-1640in order to determine a time delay during transmission. Based on thistime delay and the periodicity of the heartbeat signal, a prediction maybe made as to when the next heartbeat signal may be transmitted by themaster processor chip 1610. The processor chips 1620-1640 may then timetheir own transmissions of their own heartbeat signals to their directlycoupled processor chips to coincide, approximately, with the predictedtransmission time of the heartbeat signal from the master processor chip1610. Thus, during a next cycle of the heartbeat synchronizationoperation, the processor chips 1620-1640 will transmit their ownheartbeat signal at approximately the same time as the master processorchip 1610 again transmits its heartbeat signal to processor chips1620-1640. The processor chips 1610-1640 may continue to transmit theirheartbeat signals until it is determined that the heartbeatsynchronization operation is to be terminated.

As a result of the above process, at the end of the cycle shown in FIG.16, processor chips 1610-1640 are considered to be synchronized witheach other within a given tolerance. Thus, these processor chips1610-1640 are shaded in FIG. 16 to illustrate this synchronization whilenon-shaded processor chips of the computing cluster are still notsynchronized at this point in time. It should be appreciated that witheach subsequent receipt of a heartbeat signal during the heartbeatsynchronization operation, the processor chips 1620-1640 may refinetheir prediction of when the master processor chip 1610 will transmitthe next heartbeat signal and, as a result, adjust the timing of theirown heartbeat signals if necessary.

FIG. 17 is an exemplary diagram illustrating a second cycle of aheartbeat synchronization operation executed in the computing cluster ofFIG. 15 in accordance with one illustrative embodiment. As shown in FIG.17, processor chips 1630 and 1640 in this second cycle transmit theirown heartbeat signals, at approximately the same time as the masterprocessor chip 1610 transmits its heartbeat signal, to processor chips1710 and 1720 in their own respective processor books. In addition,processor chip 1640 is directly coupled to processor chip 1730 inanother processor book of supernode B. Thus, processor chip 1640 alsotransmits its heartbeat signal to processor chip 1730.

Again, the timestamp of the heartbeat signals from processor chips 1630and 1640 may be compared with a time at which the heartbeat signal wasreceived by the processor chips 1710-1730 in order to determine a timedelay during transmission. Based on this time delay and the periodicityof the heartbeat signal, a prediction may be made as to when the nextheartbeat signal may be transmitted by the master processor chip 1610and thus, the processor chips 1620-1640. The processor chips 1710-1730may then time their own transmissions of their own heartbeat signals totheir directly coupled processor chips to coincide, approximately, withthe predicted transmission time of the heartbeat signal from theprocessor chips 1610-1640. Thus, during a next cycle of the heartbeatsynchronization operation, the processor chips 1710-1730 will transmittheir own heartbeat signal at approximately the same time as theprocessor chips 1610-1640 again transmit their heartbeat signals. Again,the processor chips 1610-1640 and 1710-1730 may continue to transmittheir heartbeat signals until it is determined that the heartbeatsynchronization operation is to be terminated.

As a result of the above process, at the end of the cycle shown in FIG.17, processor chips 1610-1640 are considered to be synchronized from aprevious cycle and processor chips 1710-1730 are considered to besynchronized with each other and processor chips 1610-1640 based on thedepicted cycle within a given tolerance. Thus, the processor chips1610-1640 are dot-shaded in FIG. 17 and processor chips 1710-1730 aregray-shaded to illustrate this synchronization while non-shadedprocessor chips of the computing cluster are still not synchronized atthis point in time. Again, it should be appreciated that with eachsubsequent receipt of a heartbeat signal during the heartbeatsynchronization operation, the processor chips 1620-1640 and 1710-1730may refine their prediction of when the master processor chip 1610 willtransmit the next heartbeat signal and, as a result, adjust the timingof their own heartbeat signals if necessary.

FIG. 18 is an exemplary diagram illustrating a third cycle of aheartbeat synchronization operation executed in the computing cluster ofFIG. 15 in accordance with one illustrative embodiment. As shown in FIG.18, in the next cycle of the heartbeat synchronization operation, theprocessor chip 1730 transmits its own heartbeat signal to processorchips 1810 in the same processor book at approximately the same time asthe processor chips 1610-1640 and 1710-1720 transmit their heartbeatsignals. Processor chips 1810 process the heartbeat signal fromprocessor chip 1730 in a similar manner as previously described tothereby synchronize their own heartbeat signals. As a result of thisthird cycle, all of the processor chips in the computing cluster 1500 inFIG. 15 have had their heartbeat signals synchronized. Additional cyclesmay be used to allow for refinement of the timing of the heartbeatsignals, but essentially an entire computing cluster in a MTFGinterconnect architecture, regardless of the size of the computingcluster, may be synchronized in this manner in approximately 3 cycles ofthe heartbeat synchronization operation.

Once the processor chips in the computing cluster are synchronized inthis manner, the master processor chip, having allowed sufficient timefor the heartbeat synchronization operation to complete, sends out atermination message to each of the processor chips to inform them toexit the heartbeat synchronization operation state. The heartbeatsynchronization logic of the processor chips may then exit the heartbeatsynchronization operation state and may then commence using theirheartbeat signals to generate an internal system clock signal for usewith their corresponding processors or cores. As a result, the internalsystem clock signals are synchronized with the internal clock signals ofthe other processor chips in the same computing cluster.

The generation of the internal system clock signal based on theheartbeat signal may be performed in any number of ways. In oneillustrative embodiment, the heartbeat signal itself serves as theinternal system clock signal with the periodicity of the heartbeatsignal representing the frequency of the internal system clock signal.Alternatively, if a clock frequency was specified in the originalheartbeat signal from the master processor chip, upon the next heartbeatsignal being transmitted by the processor chip, an internal system clocksignal having a frequency corresponding to the frequency specified inthe original heartbeat signal from the master processor chip may bestarted. Mechanisms are available in the art for varying the frequencyof clock signals and any suitable circuitry of this nature may be usedwith the illustrative embodiments.

It should be appreciated that some circumstances may lead to theheartbeat signal and/or the internal system clock signals of theprocessor chips drifting out of synchronization. Thus, the heartbeatsynchronization logic of the processor chips may further monitorreceived heartbeat signals to determine if the timing of the heartbeatsignals does not coincide with the generation of the processor chip'sown heartbeat signal. If a timing difference between a receivedheartbeat signal and the processor chip's own heartbeat signal, takinginto account transmission delays as discussed above, is greater than atolerance or pre-established threshold value, then that processor chipmay initiate the heartbeat synchronization operation described in FIGS.15-18.

As discussed above, each of the processor chips, in accordance with oneillustrative embodiment, includes heartbeat synchronization logic forfacilitating the operations described above with regard to FIGS. 15-18.FIG. 19 is an exemplary block diagram illustrating a processor chip 1900with heartbeat synchronization logic in accordance with one illustrativeembodiment. The processor chip 1900 in FIG. 19 corresponds to theprocessor chip of FIG. 3 with the exception of the addition of heartbeatsignal synchronization logic 1910 and heartbeat signal generator 1920.The other elements in FIG. 19 corresponding to elements in FIG. 3operate in a same manner as described above with regard to FIG. 3,unless otherwise indicated hereafter.

As shown in FIG. 19, heartbeat signal synchronization logic 1910provides the logic for determining when to transmit a heartbeat signalbased on received heartbeat signals, when to initiate a heartbeat signalsynchronization operation if necessary, and the other operationspreviously discussed above. The heartbeat signal generator 1920 actuallygenerates and transmits the heartbeat signal using the Z, L, and D buses328-332. Logic (not shown) may be integrated into the processor chip1900 for generating an internal system clock signal based on theheartbeat signal generated by the heartbeat signal generator 1920.

FIG. 20 is a flowchart outlining an exemplary operation in a processorchip for performing a heartbeat synchronization process in accordancewith one illustrative embodiment. The operation outlined in FIG. 20 maybe implemented, for example, by logic of a processor chip, such asheartbeat signal synchronization logic 1910, heartbeat signal generatorlogic 1920, and other integrated logic of a processor chip.

As shown in FIG. 20, the operation starts with receiving a heartbeatsynchronization operation initialization message (step 2010). Inresponse, the processor chip enters a synchronization operation state(step 2015). The entry of such a state may involve, for example,temporarily suspending any processing being performed by the processorchip, quiescing I/O operations, or the like. The processor chip, via therouting table data structures, identifies those other processor chipsthat are directly coupled to it and which are in a same computingcluster (step 2020). Once the processor chip enters the synchronizationoperation state and has determined its directly coupled processor chips,it may communicate back to the source of the initialization message areadiness to perform the synchronization operation (step 2025).

The processor chip then receives a heartbeat signal from anotherprocessor chip (step 2030). Based on the heartbeat signal, the processorchip determines a timing of a next heartbeat signal from the otherprocessor chip (step 2035). The processor chip then transmits its ownheartbeat signal to the identified directly coupled processor chips(step 2040). The processor chip then determines if a heartbeatsynchronization operation termination message has been received (step2045). If not, the operation returns to step 2030.

If a heartbeat synchronization operation termination message has beenreceived, the processor chip may exit the heartbeat synchronizationoperation state (step 2050) and generate an internal system clock signalbased on its own heartbeat signal (step 2055). The processor chip maythen resume any temporarily suspended processes as well perform othernormal operations using the newly synchronized internal system clocksignal (step 2060). The operation then terminates.

Again, while the operation outlined in FIG. 20 makes reference toidentifying directly coupled processor chips using the routing tabledata structures, the illustrative embodiments are not limited to such.Rather, in an alternative illustrative embodiment, the heartbeat signalsmay be broadcast to all directly coupled processor chips through allports associated with the ISR without having to perform a lookupoperation in the routing table data structures.

FIG. 21 is a flowchart outlining an exemplary operation for monitoringheartbeat signals to determine if a heartbeat synchronization process isto be performed in accordance with one illustrative embodiment. Theoperation outlined in FIG. 20 may be implemented, for example, by logicof a processor chip, such as heartbeat signal synchronization logic 1910in FIG. 19 or the like. As shown in FIG. 21, the operation starts withreceiving a heartbeat signal from another processor chip (step 2110). Atime of transmission of the received heartbeat signal is determinedbased on timestamp information in the heartbeat signal and a time ofreceipt of the heartbeat signal (step 2115). The time of transmission ofthe received heartbeat signal is compared to a timestamp of a lastheartbeat signal transmitted by the current processor chip (step 2120).

The processor chip calculates a difference in the times (step 2125) andcompares this difference to a predetermined threshold value (step 2130).If the difference meets or exceeds the predetermined threshold value(step 2135), the processor chip initiates a heartbeat synchronizationoperation (step 2140) such as that described in FIGS. 15-20 above andthe operation terminates. If the difference does not meet or exceed thepredetermined threshold value, the operation terminates. This processmay be repeated for each received heartbeat signal while the processorchip is not in a heartbeat synchronization operation state.

Thus, the illustrative embodiments provide a highly-configurable,scalable system that integrates computing, storage, networking, andsoftware. The illustrative embodiments provide for a multi-tierfull-graph interface architecture that improves communicationperformance for parallel or distributed programs and improves theproductivity of the programmer and system. With such an architecture,and the additional mechanisms of the illustrative embodiments describedherein, a multi-tiered full-graph interface is provided in which maximumbandwidth is provided to each of the processors, or nodes such thatenhanced performance of parallel or distributed programs is achieved.Moreover, the illustrative embodiments provide mechanisms for providinga cluster-wide system clock through the synchronization of heartbeatsignals transmitted between the processor chips of the MTFG interconnectarchitecture.

It should be appreciated that the illustrative embodiments may take theform of an entirely hardware embodiment, an entirely software embodimentor an embodiment containing both hardware and software elements. In oneexemplary embodiment, the mechanisms of the illustrative embodiments areimplemented in software, which includes but is not limited to firmware,resident software, microcode, etc.

Furthermore, the illustrative embodiments may take the form of acomputer program product accessible from a computer-usable orcomputer-readable medium providing program code for use by or inconnection with a computer or any instruction execution system. For thepurposes of this description, a computer-usable or computer-readablemedium can be any apparatus that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device.

The medium may be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk-read only memory (CD-ROM), compactdisk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers. Network adapters mayalso be coupled to the system to enable the data processing system tobecome coupled to other data processing systems or remote printers orstorage devices through intervening private or public networks. Modems,cable modem and Ethernet cards are just a few of the currently availabletypes of network adapters.

The description of the present invention has been presented for purposesof illustration and description, and is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method, in a computing cluster comprising a plurality of processorchips, for providing a cluster-wide system clock signal, comprising:synchronizing heartbeat signals transmitted by each of the processorchips in the plurality of processor chips such that each processor chipin the plurality of processor chips transmits a heartbeat signal atapproximately a same time; and generating, in each processor chip of theplurality of processor chips, an internal system clock signal based on aheartbeat signal transmitted by the processor chip, wherein throughsynchronization of the heartbeat signals the internal system clocksignals of each processor chip of the plurality of processor chips aresynchronized.
 2. The method of claim 1, wherein the computing clustercomprises a multi-tiered full graph interconnect architecture dataprocessing system having a plurality of supernodes, each supernodehaving one or more processor books, and each processor book having oneor more processor chips of the plurality of processor chips.
 3. Themethod of claim 1, wherein synchronizing heartbeat signals transmittedby each of the processor chips comprises: transmitting, from a firstprocessor chip, a first heartbeat signal to at least one secondprocessor chip directly coupled to the first processor chip; andtransmitting, in response to receiving the first heartbeat signal, fromthe at least one second processor chip, a second heartbeat signal to atleast one third processor chip directly coupled to the at least onesecond processor chip.
 4. The method of claim 3, wherein the secondheartbeat signal is timed to be transmitted at approximately a same timeas the first heartbeat signal is re-transmitted to the at least onesecond processor chip.
 5. The method of claim 3, wherein transmittingthe first heartbeat signal to at least one second processor chipcomprises transmitting the first heartbeat signal on the ports or physassociated with the first processor chip to second processor chipscoupled to the ports or phys.
 6. The method of claim 3, whereintransmitting the first heartbeat signal to at least one second processorchip comprises: performing a lookup operation in at least one routingtable data structure to identify second processor chips directly coupledto the first processor chip; and transmitting the first heartbeat signalto second processor chips that are directly coupled to the firstprocessor chip based on results of the lookup operation.
 7. The methodof claim 6, wherein performing the lookup operation further comprises:determining if a processor chip that is directly coupled to the firstprocessor chip is in an error state; and eliminating the processor chipthat is in an error state from the second processor chips.
 8. The methodof claim 3, wherein transmitting a second heartbeat signal comprises:predicting a time at which the first processor chip will re-transmit thefirst heartbeat signal; and timing the transmitting of the secondheartbeat signal based on the predicted time at which the firstprocessor chip will re-transmit the first heartbeat signal.
 9. Themethod of claim 8, wherein the first heartbeat signal includes atimestamp of when the heartbeat signal was transmitted by the firstprocessor chip, and wherein predicting a time at which the firstprocessor chip will re-transmit the first heartbeat signal comprisesdetermining a delay during transmission of the first heartbeat signaland using the delay to predict when the first heartbeat signal will bere-transmitted.
 10. The method of claim 1, wherein the method isinitiated in response to one of a user input requesting the method to beperformed, a type of application or job that is to be processed by thecomputing cluster, or a determination that synchronization of at leasttwo processor chips in the computing cluster are sufficiently out ofsynchronization with each other.
 11. The method of claim 1, wherein theheartbeat signal comprises header information identifying at least oneidentifier of a source processor chip of the heartbeat signal.
 12. Themethod of claim 1, further comprising: using the internal system clocksignal to time processing of instructions by processors of the processorchip.
 13. The method of claim 1, further comprising: monitoring, in eachprocessor chip, receipt of heartbeat signals from directly coupled otherprocessor chips in the plurality of processor chips; determining if aheartbeat signal from any of the directly coupled other processor chipsis out of synchronization with a heartbeat signal of the processor chip;and initiating the synchronizing heartbeat signals operation in responseto the determination indicating that a heartbeat signal of a directlycoupled other processor chip is out of synchronization with theheartbeat signal of the processor chip.
 14. The method of claim 13,wherein determining if a heartbeat signal from any of the directlycoupled other processor chips is out of synchronization with a heartbeatsignal of the processor chip comprises determining a difference intimestamps of the heartbeat signals and comparing the difference to athreshold, wherein if the difference is equal to or greater than thethreshold, the synchronizing heartbeat signals operation is initiated.15. The method of claim 1, further comprising: initiating, by a masterprocessor chip in the plurality of processor chips, a heartbeatsynchronization operation; performing the heartbeat synchronizationoperation; and broadcasting an end of the heartbeat synchronizationoperation in response to the performing of the heartbeat synchronizationoperation being completed, wherein generating the internal system clocksignal is performed in response to receiving the end of the heartbeatsynchronization operation.
 16. The method of claim 1, wherein one ormore processor chips in the plurality of processor chips are provided ina first processor book and one or more processor chips in the pluralityof processor chips are provided in a second processor book.
 17. Themethod of claim 1, wherein the first processor book is in a firstsupernode and the second processor book is in a second supernode.
 18. Acomputer program product comprising a computer useable storage mediumhaving a computer readable program stored thereon, wherein the computerreadable program, when executed in a data processing system, causes thedata processing system to: synchronize heartbeat signals transmitted byeach processor chip in a plurality of processor chips such that eachprocessor chip in the plurality of processor chips transmits a heartbeatsignal at approximately a same time; and generates, in each processorchip of the plurality of processor chips, an internal system clocksignal based on a heartbeat signal transmitted by the processor chip,wherein through synchronization of the heartbeat signals the internalsystem clock signals of each processor chip of the plurality ofprocessor chips are synchronized.
 19. The computer program product ofclaim 18, wherein the computer readable program causes the dataprocessing system to synchronize heartbeat signals transmitted by eachof the processor chips by: transmitting, from a first processor chip, afirst heartbeat signal to at least one second processor chip directlycoupled to the first processor chip; and transmitting, in response toreceiving the first heartbeat signal, from the at least one secondprocessor chip, a second heartbeat signal to at least one thirdprocessor chip directly coupled to the at least one second processorchip.
 20. The computer program product of claim 18, wherein the computerreadable program causes the data processing system to transmit a secondheartbeat signal by: predicting a time at which the first processor chipwill re-transmit the first heartbeat signal; and timing the transmittingof the second heartbeat signal based on the predicted time at which thefirst processor chip will re-transmit the first heartbeat signal.